diff --git a/doc/src/sgml/Makefile b/doc/src/sgml/Makefile
index e1ba2796c336f8d2580125389c45bdf9cc5a3f2f..42551d240749e587b25318d546771f602300a239 100644
--- a/doc/src/sgml/Makefile
+++ b/doc/src/sgml/Makefile
@@ -2,7 +2,7 @@
#
# PostgreSQL documentation makefile
#
-# $Header: /cvsroot/pgsql/doc/src/sgml/Makefile,v 1.56 2003/03/25 16:15:35 petere Exp $
+# $Header: /cvsroot/pgsql/doc/src/sgml/Makefile,v 1.57 2003/04/10 01:22:44 petere Exp $
#
#----------------------------------------------------------------------------
@@ -77,7 +77,7 @@ all: html
.PHONY: html
-html: postgres.sgml $(ALLSGML) stylesheet.dsl catalogs.gif connections.gif
+html: postgres.sgml $(ALLSGML) stylesheet.dsl
@rm -f *.html
$(JADE) $(JADEFLAGS) $(SGMLINCLUDE) $(CATALOG) -d stylesheet.dsl -i output-html -t sgml $<
@@ -114,8 +114,6 @@ features-unsupported.sgml: $(top_srcdir)/src/backend/catalog/sql_feature_package
%.rtf: %.sgml $(ALLSGML) stylesheet.dsl
$(JADE) $(JADEFLAGS) $(SGMLINCLUDE) $(CATALOG) -d stylesheet.dsl -t rtf -V rtf-backend -i output-print $<
-postgres.rtf: catalogs.gif connections.gif
-
# TeX
# Regular TeX and pdfTeX have slightly differing requirements, so we
# need to distinguish the path we're taking.
@@ -123,13 +121,9 @@ postgres.rtf: catalogs.gif connections.gif
%.tex-ps: %.sgml $(ALLSGML) stylesheet.dsl
$(JADE) $(JADEFLAGS) $(SGMLINCLUDE) $(CATALOG) -d stylesheet.dsl -t tex -V tex-backend -i output-print -V texdvi-output -o $@ $<
-postgres.tex-ps: catalogs.eps connections.eps
-
%.tex-pdf: %.sgml $(ALLSGML) stylesheet.dsl
$(JADE) $(JADEFLAGS) $(SGMLINCLUDE) $(CATALOG) -d stylesheet.dsl -t tex -V tex-backend -i output-print -V texpdf-output -o $@ $<
-postgres.tex-pdf: catalogs.pdf connections.pdf
-
%.dvi: %.tex-ps
@rm -f $*.aux $*.log
jadetex $<
diff --git a/doc/src/sgml/arch-pg.sgml b/doc/src/sgml/arch-pg.sgml
deleted file mode 100644
index 21dbf58685eeebb7931357dcbe9b109fe8cbda9a..0000000000000000000000000000000000000000
--- a/doc/src/sgml/arch-pg.sgml
+++ /dev/null
@@ -1,116 +0,0 @@
-<Chapter Id="arch-pg">
- <TITLE>Architecture</TITLE>
-
-<Sect1 id="arch-pg-concepts">
-<Title><ProductName>PostgreSQL</ProductName> Architectural Concepts</Title>
-
-<Para>
- Before we begin, you should understand the basic
- <ProductName>PostgreSQL</ProductName> system architecture. Understanding how the
- parts of <ProductName>PostgreSQL</ProductName> interact will make the next chapter
- somewhat clearer.
- In database jargon, <ProductName>PostgreSQL</ProductName> uses a simple "process
- per-user" client/server model. A <ProductName>PostgreSQL</ProductName> session
- consists of the following cooperating Unix processes (programs):
-
-<ItemizedList>
-<ListItem>
-<Para>
- A supervisory daemon process (the <Application>postmaster</Application>),
-</Para>
-</ListItem>
-<ListItem>
-<Para>
- the user's frontend application (e.g., the <Application>psql</Application> program), and
-</Para>
-</ListItem>
-<ListItem>
-<Para>
- one or more backend database servers (the <Application>postgres</Application> process itself).
-</Para>
-</ListItem>
-</ItemizedList>
-</para>
-<Para>
- A single <Application>postmaster</Application> manages a given collection of
- databases on a single host. Such a collection of
- databases is called a cluster (of databases). A frontend
- application that wishes to access a given database
- within a cluster makes calls to an interface library (e.g., <application>libpq</>)
- that is linked into the application.
- The library sends user requests over the network to the
- <Application>postmaster</Application>
-(<XRef LinkEnd="PGARCH-CONNECTIONS">(a)),
-which in turn starts a new backend server process
-(<XRef LinkEnd="PGARCH-CONNECTIONS">(b))
-
-<figure id="PGARCH-CONNECTIONS">
- <title>How a connection is established</title>
-
- <mediaobject>
- <imageobject>
- <imagedata align="center" fileref="connections">
- </imageobject>
- </mediaobject>
-</figure>
-
- and connects the frontend process to the new server
-(<XRef LinkEnd="PGARCH-CONNECTIONS">(c)).
-From that point on, the frontend process and the backend
- server communicate without intervention by the
- <Application>postmaster</Application>. Hence, the <Application>postmaster</Application> is always running, waiting
- for connection requests, whereas frontend and backend processes
- come and go. The <FileName>libpq</FileName> library allows a single
- frontend to make multiple connections to backend processes.
- However, each backend process is a single-threaded process that can
- only execute one query at a time; so the communication over any one
- frontend-to-backend connection is single-threaded.
-</Para>
-
-<Para>
- One implication of this architecture is that the
- <Application>postmaster</Application> and the backend always run on the
- same machine (the database server), while the frontend
- application may run anywhere. You should keep this
- in mind,
- because the files that can be accessed on a client
- machine may not be accessible (or may only be accessed
- using a different path name) on the database server
- machine.
-</Para>
-
-<Para>
- You should also be aware that the <Application>postmaster</Application> and
- <application>postgres</> servers run with the user ID of the <ProductName>PostgreSQL</ProductName>
- <quote>superuser</>.
-Note that the <ProductName>PostgreSQL</ProductName> superuser does not
-have to be any particular user (e.g., a user named
-<literal>postgres</literal>), although many systems are installed that way.
-Furthermore, the <ProductName>PostgreSQL</ProductName> superuser should
-definitely not be the Unix superuser, <literal>root</literal>!
-It is safest if the <ProductName>PostgreSQL</ProductName> superuser is an
-ordinary, unprivileged user so far as the surrounding Unix system is
-concerned.
- In any case, all files relating to a database should belong to
- this <ProductName>Postgres</ProductName> superuser.
-</Para>
-</sect1>
-</Chapter>
-
-<!-- Keep this comment at the end of the file
-Local variables:
-mode:sgml
-sgml-omittag:nil
-sgml-shorttag:t
-sgml-minimize-attributes:nil
-sgml-always-quote-attributes:t
-sgml-indent-step:1
-sgml-indent-tabs-mode:nil
-sgml-indent-data:t
-sgml-parent-document:nil
-sgml-default-dtd-file:"./reference.ced"
-sgml-exposed-tags:nil
-sgml-local-catalogs:("/usr/share/sgml/catalog")
-sgml-local-ecat-files:nil
-End:
--->
diff --git a/doc/src/sgml/dfunc.sgml b/doc/src/sgml/dfunc.sgml
index ae30dd1fa967eaf9a54d5b5d259e38d5e23fd8ba..3898a2bc1765dc2758427ba2a97b5279ad19dadc 100644
--- a/doc/src/sgml/dfunc.sgml
+++ b/doc/src/sgml/dfunc.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/dfunc.sgml,v 1.24 2003/03/25 16:15:35 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/dfunc.sgml,v 1.25 2003/04/10 01:22:44 petere Exp $
-->
<sect2 id="dfunc">
@@ -14,7 +14,8 @@ $Header: /cvsroot/pgsql/doc/src/sgml/dfunc.sgml,v 1.24 2003/03/25 16:15:35 peter
</para>
<para>
- For more information you should read the documentation of your
+ For information beyond what is contained in this section
+ you should read the documentation of your
operating system, in particular the manual pages for the C compiler,
<command>cc</command>, and the link editor, <command>ld</command>.
In addition, the <productname>PostgreSQL</productname> source code
@@ -47,13 +48,10 @@ $Header: /cvsroot/pgsql/doc/src/sgml/dfunc.sgml,v 1.24 2003/03/25 16:15:35 peter
here.
</para>
- <para>
-
<!--
- Note: Reading GNU Libtool sources is generally a good way of figuring out
- this information. The methods used within
- <productname>PostgreSQL</> source code are not
- necessarily ideal.
+ Note: Reading GNU Libtool sources is generally a good way of
+ figuring out this information. The methods used within PostgreSQL
+ source code are not necessarily ideal.
-->
<variablelist>
@@ -160,7 +158,7 @@ cc -shared -o foo.so foo.o
<indexterm><primary>MacOS X</></>
<listitem>
<para>
- Here is a sample. It assumes the developer tools are installed.
+ Here is an example. It assumes the developer tools are installed.
<programlisting>
cc -c foo.c
cc -bundle -flat_namespace -undefined suppress -o foo.so foo.o
@@ -271,17 +269,13 @@ gcc -shared -o foo.so foo.o
</varlistentry>
</variablelist>
- </para>
<tip>
<para>
- If you want to package your extension modules for wide distribution
- you should consider using <ulink
- url="http://www.gnu.org/software/libtool/"><productname>GNU
- Libtool</productname></ulink> for building shared libraries. It
- encapsulates the platform differences into a general and powerful
- interface. Serious packaging also requires considerations about
- library versioning, symbol resolution methods, and other issues.
+ If this is too complicated for you, you should consider using
+ <ulink url="http://www.gnu.org/software/libtool/"><productname>GNU
+ Libtool</productname></ulink>, which hides the platform differences
+ behind a uniform interface.
</para>
</tip>
diff --git a/doc/src/sgml/extend.sgml b/doc/src/sgml/extend.sgml
index 1367f16d784f080d06f25da0c891cb958c569fd5..60ea4acb469ca0a28dcd17a0d94998d0a15bd30e 100644
--- a/doc/src/sgml/extend.sgml
+++ b/doc/src/sgml/extend.sgml
@@ -1,9 +1,9 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.20 2003/03/25 16:15:36 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.21 2003/04/10 01:22:44 petere Exp $
-->
<chapter id="extend">
- <title>Extending <acronym>SQL</acronym>: An Overview</title>
+ <title>Extending <acronym>SQL</acronym></title>
<indexterm zone="extend">
<primary>extending SQL</primary>
@@ -17,22 +17,22 @@ $Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.20 2003/03/25 16:15:36 pete
<itemizedlist spacing="compact" mark="bullet">
<listitem>
<para>
- functions
+ functions (starting in <xref linkend="xfunc">)
</para>
</listitem>
<listitem>
<para>
- data types
+ data types (starting in <xref linkend="xtypes">)
</para>
</listitem>
<listitem>
<para>
- operators
+ operators (starting in <xref linkend="xoper">)
</para>
</listitem>
<listitem>
<para>
- aggregates
+ aggregates (starting in <xref linkend="xaggr">)
</para>
</listitem>
</itemizedlist>
@@ -44,30 +44,29 @@ $Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.20 2003/03/25 16:15:36 pete
<para>
<productname>PostgreSQL</productname> is extensible because its operation is
catalog-driven. If you are familiar with standard
- relational systems, you know that they store information
+ relational database systems, you know that they store information
about databases, tables, columns, etc., in what are
commonly known as system catalogs. (Some systems call
this the data dictionary). The catalogs appear to the
user as tables like any other, but the <acronym>DBMS</acronym> stores
its internal bookkeeping in them. One key difference
- between <productname>PostgreSQL</productname> and standard relational systems is
+ between <productname>PostgreSQL</productname> and standard relational database systems is
that <productname>PostgreSQL</productname> stores much more information in its
- catalogs -- not only information about tables and columns,
- but also information about its types, functions, access
+ catalogs: not only information about tables and columns,
+ but also information about data types, functions, access
methods, and so on. These tables can be modified by
- the user, and since <productname>PostgreSQL</productname> bases its internal operation
+ the user, and since <productname>PostgreSQL</productname> bases its operation
on these tables, this means that <productname>PostgreSQL</productname> can be
extended by users. By comparison, conventional
database systems can only be extended by changing hardcoded
- procedures within the <acronym>DBMS</acronym> or by loading modules
+ procedures in the source code or by loading modules
specially written by the <acronym>DBMS</acronym> vendor.
</para>
<para>
- <productname>PostgreSQL</productname> is also unlike most other data managers in
- that the server can incorporate user-written code into
+ The PostgreSQL server can moreover incorporate user-written code into
itself through dynamic loading. That is, the user can
- specify an object code file (e.g., a shared library) that implements a new type or function
+ specify an object code file (e.g., a shared library) that implements a new type or function,
and <productname>PostgreSQL</productname> will load it as required. Code written
in <acronym>SQL</acronym> is even more trivial to add to the server.
This ability to modify its operation <quote>on the fly</quote> makes
@@ -89,195 +88,25 @@ $Header: /cvsroot/pgsql/doc/src/sgml/extend.sgml,v 1.20 2003/03/25 16:15:36 pete
</indexterm>
<para>
- The <productname>PostgreSQL</productname> type system
- can be broken down in several ways.
- Types are divided into base types and composite types.
+ Data types are divided into base types and composite types.
Base types are those, like <type>int4</type>, that are implemented
in a language such as C. They generally correspond to
- what are often known as <firstterm>abstract data types</firstterm>; <productname>PostgreSQL</productname>
+ what are often known as abstract data types. <productname>PostgreSQL</productname>
can only operate on such types through methods provided
by the user and only understands the behavior of such
types to the extent that the user describes them.
Composite types are created whenever the user creates a
- table.
- </para>
-
- <para>
- <productname>PostgreSQL</productname> stores these types
- in only one way (within the
- file that stores all rows of a table) but the
+ table. The
user can <quote>look inside</quote> at the attributes of these types
- from the query language and optimize their retrieval by
- (for example) defining indexes on the attributes.
- <productname>PostgreSQL</productname> base types are further
- divided into built-in
- types and user-defined types. Built-in types (like
- <type>int4</type>) are those that are compiled
- into the system.
- User-defined types are those created by the user in the
- manner to be described later.
+ from the query language.
</para>
</sect1>
- <sect1 id="pg-system-catalogs">
- <title>About the <productname>PostgreSQL</productname> System Catalogs</title>
-
- <indexterm zone="pg-system-catalogs">
- <primary>catalogs</primary>
- </indexterm>
-
- <para>
- Having introduced the basic extensibility concepts, we
- can now take a look at how the catalogs are actually
- laid out. You can skip this section for now, but some
- later sections will be incomprehensible without the
- information given here, so mark this page for later
- reference.
- All system catalogs have names that begin with
- <literal>pg_</literal>.
- The following tables contain information that may be
- useful to the end user. (There are many other system
- catalogs, but there should rarely be a reason to query
- them directly.)
+ &xfunc;
+ &xtypes;
+ &xoper;
+ &xaggr;
- <table tocentry="1">
- <title>PostgreSQL System Catalogs</title>
- <titleabbrev>Catalogs</titleabbrev>
- <tgroup cols="2">
- <thead>
- <row>
- <entry>Catalog Name</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry><structname>pg_database</></entry>
- <entry> databases</entry>
- </row>
- <row>
- <entry><structname>pg_class</></entry>
- <entry> tables</entry>
- </row>
- <row>
- <entry><structname>pg_attribute</></entry>
- <entry> table columns</entry>
- </row>
- <row>
- <entry><structname>pg_index</></entry>
- <entry> indexes</entry>
- </row>
- <row>
- <entry><structname>pg_proc</></entry>
- <entry> procedures/functions </entry>
- </row>
- <row>
- <entry><structname>pg_type</></entry>
- <entry> data types (both base and complex)</entry>
- </row>
- <row>
- <entry><structname>pg_operator</></entry>
- <entry> operators</entry>
- </row>
- <row>
- <entry><structname>pg_aggregate</></entry>
- <entry> aggregate functions</entry>
- </row>
- <row>
- <entry><structname>pg_am</></entry>
- <entry> access methods</entry>
- </row>
- <row>
- <entry><structname>pg_amop</></entry>
- <entry> access method operators</entry>
- </row>
- <row>
- <entry><structname>pg_amproc</></entry>
- <entry> access method support functions</entry>
- </row>
- <row>
- <entry><structname>pg_opclass</></entry>
- <entry> access method operator classes</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
- </para>
-
- <para>
- <figure float="1" id="EXTEND-CATALOGS">
- <title>The major <productname>PostgreSQL</productname> system catalogs</title>
- <mediaobject>
- <imageobject>
- <imagedata fileref="catalogs" align="center">
- </imageobject>
- </mediaobject>
- </figure>
-
- <xref linkend="catalogs"> gives a more detailed explanation of these
- catalogs and their columns. However,
- <xref linkend="EXTEND-CATALOGS">
- shows the major entities and their relationships
- in the system catalogs. (Columns that do not refer
- to other entities are not shown unless they are part of
- a primary key.)
- This diagram is more or less incomprehensible until you
- actually start looking at the contents of the catalogs
- and see how they relate to each other. For now, the
- main things to take away from this diagram are as follows:
-
- <itemizedlist spacing="compact" mark="bullet">
- <listitem>
- <para>
- In several of the sections that follow, we will
- present various join queries on the system
- catalogs that display information we need to extend
- the system. Looking at this diagram should make
- some of these join queries (which are often
- three- or four-way joins) more understandable,
- because you will be able to see that the
- columns used in the queries form foreign keys
- in other tables.
- </para>
- </listitem>
- <listitem>
- <para>
- Many different features (tables, columns,
- functions, types, access methods, etc.) are
- tightly integrated in this schema. A simple
- create command may modify many of these catalogs.
- </para>
- </listitem>
- <listitem>
- <para>
- Types and procedures
- are central to the schema.
-
- <note>
- <para>
- We use the words <firstterm>procedure</firstterm>
- and <firstterm>function</firstterm> more or less interchangeably.
- </para>
- </note>
-
- Nearly every catalog contains some reference to
- rows in one or both of these tables. For
- example, <productname>PostgreSQL</productname> frequently uses type
- signatures (e.g., of functions and operators) to
- identify unique rows of other catalogs.
- </para>
- </listitem>
- <listitem>
- <para>
- There are many columns and relationships that
- have obvious meanings, but there are many
- (particularly those that have to do with access
- methods) that do not.
- </para>
- </listitem>
- </itemizedlist>
- </para>
- </sect1>
</chapter>
<!-- Keep this comment at the end of the file
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index 01f09431454c006768d8553d3fa0a4fb906b501c..ed4d13223c67822290e84fc3d40bc7e317e90d84 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -1,4 +1,4 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/filelist.sgml,v 1.27 2003/03/25 16:15:36 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/filelist.sgml,v 1.28 2003/04/10 01:22:44 petere Exp $ -->
<!entity history SYSTEM "history.sgml">
<!entity info SYSTEM "info.sgml">
@@ -57,7 +57,6 @@
<!entity wal SYSTEM "wal.sgml">
<!-- programmer's guide -->
-<!entity arch-pg SYSTEM "arch-pg.sgml">
<!entity dfunc SYSTEM "dfunc.sgml">
<!entity ecpg SYSTEM "ecpg.sgml">
<!entity extend SYSTEM "extend.sgml">
diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml
index 30849fb9e3c5692e92667241688e2e4376c79db5..e207cdacc4e1da4a0b7f4ed43932227e3904d202 100644
--- a/doc/src/sgml/postgres.sgml
+++ b/doc/src/sgml/postgres.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.49 2003/03/25 16:15:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.50 2003/04/10 01:22:44 petere Exp $
-->
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [
@@ -210,15 +210,10 @@ $Header: /cvsroot/pgsql/doc/src/sgml/postgres.sgml,v 1.49 2003/03/25 16:15:38 pe
</para>
</partintro>
- &arch-pg;
&extend;
- &xfunc;
- &xtypes;
- &xoper;
- &xaggr;
- &rules;
&xindex;
&indexcost;
+ &rules;
&trigger;
&spi;
diff --git a/doc/src/sgml/queries.sgml b/doc/src/sgml/queries.sgml
index 1c6c1f4ae399f7c75cb6159fa88850bfbd23c81c..04029f529b49e469266606db024ba8abf0aae72e 100644
--- a/doc/src/sgml/queries.sgml
+++ b/doc/src/sgml/queries.sgml
@@ -1,4 +1,4 @@
-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.20 2003/03/13 01:30:29 petere Exp $ -->
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.21 2003/04/10 01:22:44 petere Exp $ -->
<chapter id="queries">
<title>Queries</title>
@@ -550,6 +550,78 @@ FROM (SELECT * FROM table1) AS alias_name
grouping or aggregation.
</para>
</sect3>
+
+ <sect3 id="queries-tablefunctions">
+ <title>Table Functions</title>
+
+ <indexterm zone="queries-tablefunctions"><primary>table function</></>
+
+ <para>
+ Table functions are functions that produce a set of rows, made up
+ of either base data types (scalar types) or composite data types
+ (table rows). They are used like a table, view, or subquery in
+ the <literal>FROM</> clause of a query. Columns returned by table
+ functions may be included in <literal>SELECT</>,
+ <literal>JOIN</>, or <literal>WHERE</> clauses in the same manner
+ as a table, view, or subquery column.
+ </para>
+
+ <para>
+ If a table function returns a base data type, the single result
+ column is named like the function. If the function returns a
+ composite type, the result columns get the same names as the
+ individual attributes of the type.
+ </para>
+
+ <para>
+ A table function may be aliased in the <literal>FROM</> clause,
+ but it also may be left unaliased. If a function is used in the
+ <literal>FROM</> clause with no alias, the function name is used
+ as the resulting table name.
+ </para>
+
+ <para>
+ Some examples:
+<programlisting>
+CREATE TABLE foo (fooid int, foosubid int, fooname text);
+
+CREATE FUNCTION getfoo(int) RETURNS SETOF foo AS '
+ SELECT * FROM foo WHERE fooid = $1;
+' LANGUAGE SQL;
+
+SELECT * FROM getfoo(1) AS t1;
+
+SELECT * FROM foo
+ WHERE foosubid IN (select foosubid from getfoo(foo.fooid) z
+ where z.fooid = foo.fooid);
+
+CREATE VIEW vw_getfoo AS SELECT * FROM getfoo(1);
+SELECT * FROM vw_getfoo;
+</programlisting>
+ </para>
+
+ <para>
+ In some cases it is useful to define table functions that can
+ return different column sets depending on how they are invoked.
+ To support this, the table function can be declared as returning
+ the pseudotype <type>record</>. When such a function is used in
+ a query, the expected row structure must be specified in the
+ query itself, so that the system can know how to parse and plan
+ the query. Consider this example:
+<programlisting>
+SELECT *
+ FROM dblink('dbname=mydb', 'select proname, prosrc from pg_proc')
+ AS t1(proname name, prosrc text)
+ WHERE proname LIKE 'bytea%';
+</programlisting>
+ The <literal>dblink</> function executes a remote query (see
+ <filename>contrib/dblink</>). It is declared to return
+ <type>record</> since it might be used for any kind of query.
+ The actual column set must be specified in the calling query so
+ that the parser knows, for example, what <literal>*</> should
+ expand to.
+ </para>
+ </sect3>
</sect2>
<sect2 id="queries-where">
@@ -951,7 +1023,7 @@ SELECT DISTINCT ON (<replaceable>expression</replaceable> <optional>, <replaceab
The <literal>DISTINCT ON</> clause is not part of the SQL standard
and is sometimes considered bad style because of the potentially
indeterminate nature of its results. With judicious use of
- <literal>GROUP BY</> and subselects in <literal>FROM</> the
+ <literal>GROUP BY</> and subqueries in <literal>FROM</> the
construct can be avoided, but it is often the most convenient
alternative.
</para>
diff --git a/doc/src/sgml/xaggr.sgml b/doc/src/sgml/xaggr.sgml
index 33bfd9622993122391837c53301cf8b2684f2077..101067e17565c50610c728dd1721ef681786653e 100644
--- a/doc/src/sgml/xaggr.sgml
+++ b/doc/src/sgml/xaggr.sgml
@@ -1,9 +1,9 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/xaggr.sgml,v 1.19 2003/03/25 16:15:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/xaggr.sgml,v 1.20 2003/04/10 01:22:44 petere Exp $
-->
- <chapter id="xaggr">
- <title>Extending <acronym>SQL</acronym>: Aggregates</title>
+ <sect1 id="xaggr">
+ <title>User-Defined Aggregates</title>
<indexterm zone="xaggr">
<primary>aggregate functions</primary>
@@ -22,38 +22,36 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xaggr.sgml,v 1.19 2003/03/25 16:15:38 peter
function. The state transition function is just an
ordinary function that could also be used outside the
context of the aggregate. A <firstterm>final function</firstterm>
- can also be specified, in case the desired output of the aggregate
+ can also be specified, in case the desired result of the aggregate
is different from the data that needs to be kept in the running
state value.
</para>
<para>
- Thus, in addition to the input and result data types seen by a user
+ Thus, in addition to the argument and result data types seen by a user
of the aggregate, there is an internal state-value data type that
- may be different from both the input and result types.
+ may be different from both the argument and result types.
</para>
<para>
If we define an aggregate that does not use a final function,
we have an aggregate that computes a running function of
- the column values from each row. <function>Sum</> is an
- example of this kind of aggregate. <function>Sum</> starts at
+ the column values from each row. <function>sum</> is an
+ example of this kind of aggregate. <function>sum</> starts at
zero and always adds the current row's value to
its running total. For example, if we want to make a <function>sum</>
aggregate to work on a data type for complex numbers,
we only need the addition function for that data type.
- The aggregate definition is:
+ The aggregate definition would be:
-<programlisting>
+<screen>
CREATE AGGREGATE complex_sum (
sfunc = complex_add,
basetype = complex,
stype = complex,
initcond = '(0,0)'
);
-</programlisting>
-<screen>
SELECT complex_sum(a) FROM test_complex;
complex_sum
@@ -61,43 +59,43 @@ SELECT complex_sum(a) FROM test_complex;
(34,53.9)
</screen>
- (In practice, we'd just name the aggregate <function>sum</function>, and rely on
+ (In practice, we'd just name the aggregate <function>sum</function> and rely on
<productname>PostgreSQL</productname> to figure out which kind
of sum to apply to a column of type <type>complex</type>.)
</para>
<para>
The above definition of <function>sum</function> will return zero (the initial
- state condition) if there are no non-null input values.
- Perhaps we want to return NULL in that case instead --- the SQL standard
+ state condition) if there are no nonnull input values.
+ Perhaps we want to return null in that case instead --- the SQL standard
expects <function>sum</function> to behave that way. We can do this simply by
omitting the <literal>initcond</literal> phrase, so that the initial state
- condition is NULL. Ordinarily this would mean that the <literal>sfunc</literal>
- would need to check for a NULL state-condition input, but for
+ condition is null. Ordinarily this would mean that the <literal>sfunc</literal>
+ would need to check for a null state-condition input, but for
<function>sum</function> and some other simple aggregates like <function>max</> and <function>min</>,
- it's sufficient to insert the first non-null input value into
+ it would be sufficient to insert the first nonnull input value into
the state variable and then start applying the transition function
- at the second non-null input value. <productname>PostgreSQL</productname>
- will do that automatically if the initial condition is NULL and
+ at the second nonnull input value. <productname>PostgreSQL</productname>
+ will do that automatically if the initial condition is null and
the transition function is marked <quote>strict</> (i.e., not to be called
- for NULL inputs).
+ for null inputs).
</para>
<para>
Another bit of default behavior for a <quote>strict</> transition function
is that the previous state value is retained unchanged whenever a
- NULL input value is encountered. Thus, null values are ignored. If you
- need some other behavior for NULL inputs, just define your transition
- function as non-strict, and code it to test for NULL inputs and do
+ null input value is encountered. Thus, null values are ignored. If you
+ need some other behavior for null inputs, just do not define your transition
+ function as strict, and code it to test for null inputs and do
whatever is needed.
</para>
<para>
- <function>Avg</> (average) is a more complex example of an aggregate. It requires
+ <function>avg</> (average) is a more complex example of an aggregate. It requires
two pieces of running state: the sum of the inputs and the count
of the number of inputs. The final result is obtained by dividing
these quantities. Average is typically implemented by using a
- two-element array as the transition state value. For example,
+ two-element array as the state value. For example,
the built-in implementation of <function>avg(float8)</function>
looks like:
@@ -116,7 +114,7 @@ CREATE AGGREGATE avg (
For further details see the description of the <command>CREATE
AGGREGATE</command> command in <xref linkend="reference">.
</para>
- </chapter>
+ </sect1>
<!-- Keep this comment at the end of the file
Local variables:
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 5398df7ad9229c8474fe78bffb6117cb99856951..4f9018e1d58a6a4cfd008c52522093a9bb56118a 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -1,15 +1,12 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.66 2003/03/25 16:15:38 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.67 2003/04/10 01:22:45 petere Exp $
-->
- <chapter id="xfunc">
- <title id="xfunc-title">Extending <acronym>SQL</acronym>: Functions</title>
+ <sect1 id="xfunc">
+ <title>User-Defined Functions</title>
<indexterm zone="xfunc"><primary>function</></>
- <sect1 id="xfunc-intro">
- <title>Introduction</title>
-
<para>
<productname>PostgreSQL</productname> provides four kinds of
functions:
@@ -17,24 +14,25 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.66 2003/03/25 16:15:38 peter
<itemizedlist>
<listitem>
<para>
- query language functions
- (functions written in <acronym>SQL</acronym>)
+ query language functions (functions written in
+ <acronym>SQL</acronym>) (<xref linkend="xfunc-sql">)
</para>
</listitem>
<listitem>
<para>
- procedural language
- functions (functions written in, for example, <application>PL/Tcl</> or <application>PL/pgSQL</>)
+ procedural language functions (functions written in, for
+ example, <application>PL/Tcl</> or <application>PL/pgSQL</>)
+ (<xref linkend="xfunc-pl">)
</para>
</listitem>
<listitem>
<para>
- internal functions
+ internal functions (<xref linkend="xfunc-internal">)
</para>
</listitem>
<listitem>
<para>
- C language functions
+ C-language functions (<xref linkend="xfunc-c">)
</para>
</listitem>
</itemizedlist>
@@ -42,10 +40,14 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.66 2003/03/25 16:15:38 peter
<para>
Every kind
- of function can take a base type, a composite type, or
+ of function can take base types, composite types, or
some combination as arguments (parameters). In addition,
every kind of function can return a base type or
- a composite type. It's easiest to define <acronym>SQL</acronym>
+ a composite type.
+ </para>
+
+ <para>
+ It's easiest to define <acronym>SQL</acronym>
functions, so we'll start with those. Examples in this section
can also be found in <filename>funcs.sql</filename>
and <filename>funcs.c</filename> in the tutorial directory.
@@ -72,14 +74,14 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.66 2003/03/25 16:15:38 peter
(Bear in mind that <quote>the first row</quote> of a multirow
result is not well-defined unless you use <literal>ORDER BY</>.)
If the last query happens
- to return no rows at all, NULL will be returned.
+ to return no rows at all, the null value will be returned.
</para>
<para>
<indexterm><primary>SETOF</><seealso>function</></>
Alternatively, an SQL function may be declared to return a set,
by specifying the function's return type
- as <literal>SETOF</literal> <replaceable>sometype</>. In this case
+ as <literal>SETOF <replaceable>sometype</></literal>. In this case
all rows of the last query's result are returned. Further details
appear below.
</para>
@@ -97,22 +99,65 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xfunc.sgml,v 1.66 2003/03/25 16:15:38 peter
<para>
Arguments to the SQL function may be referenced in the function
- body using the syntax <literal>$<replaceable>n</></>: $1 refers to
- the first argument, $2 to the second, and so on. If an argument
- is of a composite type, then the <quote>dot notation</quote>,
- e.g., <literal>$1.emp</literal>, may be used to access attributes
+ body using the syntax <literal>$<replaceable>n</></>: <literal>$1</> refers to
+ the first argument, <literal>$2</> to the second, and so on. If an argument
+ is of a composite type, then the dot notation,
+ e.g., <literal>$1.name</literal>, may be used to access attributes
of the argument.
</para>
<sect2>
- <title>Examples</title>
+ <title><acronym>SQL</acronym> Functions on Base Types</title>
+
+ <para>
+ The simplest possible <acronym>SQL</acronym> function has no arguments and
+ simply returns a base type, such as <type>integer</type>:
+
+<screen>
+CREATE FUNCTION one() RETURNS integer AS '
+ SELECT 1 AS result;
+' LANGUAGE SQL;
+
+SELECT one();
+
+ one
+-----
+ 1
+</screen>
+ </para>
+
+ <para>
+ Notice that we defined a column alias within the function body for the result of the function
+ (with the name <literal>result</>), but this column alias is not visible
+ outside the function. Hence, the result is labeled <literal>one</>
+ instead of <literal>result</>.
+ </para>
+
+ <para>
+ It is almost as easy to define <acronym>SQL</acronym> functions
+ that take base types as arguments. In the example below, notice
+ how we refer to the arguments within the function as <literal>$1</>
+ and <literal>$2</>.
+
+<screen>
+CREATE FUNCTION add_em(integer, integer) RETURNS integer AS '
+ SELECT $1 + $2;
+' LANGUAGE SQL;
+
+SELECT add_em(1, 2) AS answer;
+
+ answer
+--------
+ 3
+</screen>
+ </para>
<para>
- To illustrate a simple SQL function, consider the following,
- which might be used to debit a bank account:
+ Here is a more useful function, which might be used to debit a
+ bank account:
<programlisting>
-CREATE FUNCTION tp1 (integer, numeric) RETURNS integer AS '
+CREATE FUNCTION tf1 (integer, numeric) RETURNS integer AS '
UPDATE bank
SET balance = balance - $2
WHERE accountno = $1;
@@ -124,17 +169,17 @@ CREATE FUNCTION tp1 (integer, numeric) RETURNS integer AS '
follows:
<programlisting>
-SELECT tp1(17, 100.0);
+SELECT tf1(17, 100.0);
</programlisting>
</para>
<para>
In practice one would probably like a more useful result from the
- function than a constant <quote>1</>, so a more likely definition
+ function than a constant 1, so a more likely definition
is
<programlisting>
-CREATE FUNCTION tp1 (integer, numeric) RETURNS numeric AS '
+CREATE FUNCTION tf1 (integer, numeric) RETURNS numeric AS '
UPDATE bank
SET balance = balance - $2
WHERE accountno = $1;
@@ -148,83 +193,29 @@ CREATE FUNCTION tp1 (integer, numeric) RETURNS numeric AS '
<para>
Any collection of commands in the <acronym>SQL</acronym>
language can be packaged together and defined as a function.
- The commands can include data modification (i.e.,
+ Besides <command>SELECT</command> queries,
+ the commands can include data modification (i.e.,
<command>INSERT</command>, <command>UPDATE</command>, and
- <command>DELETE</command>) as well
- as <command>SELECT</command> queries. However, the final command
+ <command>DELETE</command>). However, the final command
must be a <command>SELECT</command> that returns whatever is
specified as the function's return type. Alternatively, if you
want to define a SQL function that performs actions but has no
useful value to return, you can define it as returning <type>void</>.
- In that case it must not end with a <command>SELECT</command>.
+ In that case, the function body must not end with a <command>SELECT</command>.
For example:
-<programlisting>
-CREATE FUNCTION clean_EMP () RETURNS void AS '
- DELETE FROM EMP
- WHERE EMP.salary <= 0;
+<screen>
+CREATE FUNCTION clean_emp() RETURNS void AS '
+ DELETE FROM emp
+ WHERE salary <= 0;
' LANGUAGE SQL;
-SELECT clean_EMP();
-</programlisting>
+SELECT clean_emp();
-<screen>
clean_emp
-----------
(1 row)
-</screen>
- </para>
-
- </sect2>
-
- <sect2>
- <title><acronym>SQL</acronym> Functions on Base Types</title>
-
- <para>
- The simplest possible <acronym>SQL</acronym> function has no arguments and
- simply returns a base type, such as <type>integer</type>:
-
-<programlisting>
-CREATE FUNCTION one() RETURNS integer AS '
- SELECT 1 as RESULT;
-' LANGUAGE SQL;
-
-SELECT one();
-</programlisting>
-
-<screen>
- one
------
- 1
-</screen>
- </para>
-
- <para>
- Notice that we defined a column alias within the function body for the result of the function
- (with the name <literal>RESULT</>), but this column alias is not visible
- outside the function. Hence, the result is labeled <literal>one</>
- instead of <literal>RESULT</>.
- </para>
-
- <para>
- It is almost as easy to define <acronym>SQL</acronym> functions
- that take base types as arguments. In the example below, notice
- how we refer to the arguments within the function as <literal>$1</>
- and <literal>$2</>:
-
-<programlisting>
-CREATE FUNCTION add_em(integer, integer) RETURNS integer AS '
- SELECT $1 + $2;
-' LANGUAGE SQL;
-
-SELECT add_em(1, 2) AS answer;
-</programlisting>
-
-<screen>
- answer
---------
- 3
</screen>
</para>
</sect2>
@@ -237,22 +228,27 @@ SELECT add_em(1, 2) AS answer;
types, we must not only specify which
argument we want (as we did above with <literal>$1</> and <literal>$2</literal>) but
also the attributes of that argument. For example, suppose that
- <type>EMP</type> is a table containing employee data, and therefore
+ <type>emp</type> is a table containing employee data, and therefore
also the name of the composite type of each row of the table. Here
- is a function <function>double_salary</function> that computes what your
+ is a function <function>double_salary</function> that computes what someone's
salary would be if it were doubled:
-<programlisting>
-CREATE FUNCTION double_salary(EMP) RETURNS integer AS '
+<screen>
+CREATE TABLE emp (
+ name text,
+ salary integer,
+ age integer,
+ cubicle point
+);
+
+CREATE FUNCTION double_salary(emp) RETURNS integer AS '
SELECT $1.salary * 2 AS salary;
' LANGUAGE SQL;
-SELECT name, double_salary(EMP) AS dream
- FROM EMP
- WHERE EMP.cubicle ~= point '(2,1)';
-</programlisting>
+SELECT name, double_salary(emp) AS dream
+ FROM emp
+ WHERE emp.cubicle ~= point '(2,1)';
-<screen>
name | dream
------+-------
Sam | 2400
@@ -269,28 +265,29 @@ SELECT name, double_salary(EMP) AS dream
<para>
It is also possible to build a function that returns a composite type.
This is an example of a function
- that returns a single <type>EMP</type> row:
+ that returns a single <type>emp</type> row:
<programlisting>
-CREATE FUNCTION new_emp() RETURNS EMP AS '
+CREATE FUNCTION new_emp() RETURNS emp AS '
SELECT text ''None'' AS name,
1000 AS salary,
25 AS age,
point ''(2,2)'' AS cubicle;
' LANGUAGE SQL;
</programlisting>
- </para>
- <para>
In this case we have specified each of the attributes
- with a constant value, but any computation or expression
+ with a constant value, but any computation
could have been substituted for these constants.
+ </para>
+
+ <para>
Note two important things about defining the function:
<itemizedlist>
<listitem>
<para>
- The target list order must be exactly the same as
+ The select list order in the query must be exactly the same as
that in which the columns appear in the table associated
with the composite type. (Naming the columns, as we did above,
is irrelevant to the system.)
@@ -315,13 +312,15 @@ ERROR: function declared to return emp returns varchar instead of text at colum
function, as described below. It can also be called in the context
of an SQL expression, but only when you
extract a single attribute out of the row or pass the entire row into
- another function that accepts the same composite type. For example,
+ another function that accepts the same composite type.
+ </para>
-<programlisting>
-SELECT (new_emp()).name;
-</programlisting>
+ <para>
+ This is an example for how to extract an attribute out of a row type:
<screen>
+SELECT (new_emp()).name;
+
name
------
None
@@ -340,29 +339,24 @@ ERROR: parser: parse error at or near "."
functional notation for extracting an attribute. The simple way
to explain this is that we can use the
notations <literal>attribute(table)</> and <literal>table.attribute</>
- interchangeably:
+ interchangeably.
-<programlisting>
+<screen>
SELECT name(new_emp());
-</programlisting>
-<screen>
name
------
None
</screen>
-<programlisting>
---
--- this is the same as:
--- SELECT EMP.name AS youngster FROM EMP WHERE EMP.age < 30
---
-SELECT name(EMP) AS youngster
- FROM EMP
- WHERE age(EMP) < 30;
-</programlisting>
-
<screen>
+-- This is the same as:
+-- SELECT emp.name AS youngster FROM emp WHERE emp.age < 30
+
+SELECT name(emp) AS youngster
+ FROM emp
+ WHERE age(emp) < 30;
+
youngster
-----------
Sam
@@ -370,17 +364,15 @@ SELECT name(EMP) AS youngster
</para>
<para>
- Another way to use a function returning a row result is to declare a
- second function accepting a row type parameter, and pass the function
- result to it:
+ The other way to use a function returning a row result is to declare a
+ second function accepting a row type argument and pass the
+ result of the first function to it:
-<programlisting>
+<screen>
CREATE FUNCTION getname(emp) RETURNS text AS
'SELECT $1.name;'
LANGUAGE SQL;
-</programlisting>
-<screen>
SELECT getname(new_emp());
getname
---------
@@ -391,35 +383,32 @@ SELECT getname(new_emp());
</sect2>
<sect2>
- <title><acronym>SQL</acronym> Table Functions</title>
+ <title><acronym>SQL</acronym> Functions as Table Sources</title>
<para>
- A table function is one that may be used in the <command>FROM</command>
- clause of a query. All SQL language functions may be used in this manner,
+ All SQL functions may be used in the <literal>FROM</> clause of a query,
but it is particularly useful for functions returning composite types.
If the function is defined to return a base type, the table function
produces a one-column table. If the function is defined to return
- a composite type, the table function produces a column for each column
+ a composite type, the table function produces a column for each attribute
of the composite type.
</para>
<para>
Here is an example:
-<programlisting>
+<screen>
CREATE TABLE foo (fooid int, foosubid int, fooname text);
-INSERT INTO foo VALUES(1,1,'Joe');
-INSERT INTO foo VALUES(1,2,'Ed');
-INSERT INTO foo VALUES(2,1,'Mary');
+INSERT INTO foo VALUES (1, 1, 'Joe');
+INSERT INTO foo VALUES (1, 2, 'Ed');
+INSERT INTO foo VALUES (2, 1, 'Mary');
CREATE FUNCTION getfoo(int) RETURNS foo AS '
SELECT * FROM foo WHERE fooid = $1;
' LANGUAGE SQL;
SELECT *, upper(fooname) FROM getfoo(1) AS t1;
-</programlisting>
-<screen>
fooid | foosubid | fooname | upper
-------+----------+---------+-------
1 | 1 | Joe | JOE
@@ -432,35 +421,35 @@ SELECT *, upper(fooname) FROM getfoo(1) AS t1;
<para>
Note that we only got one row out of the function. This is because
- we did not say <literal>SETOF</>.
+ we did not use <literal>SETOF</>. This is described in the next section.
</para>
-
</sect2>
<sect2>
<title><acronym>SQL</acronym> Functions Returning Sets</title>
<para>
- When an SQL function is declared as returning <literal>SETOF</literal>
- <replaceable>sometype</>, the function's final
+ When an SQL function is declared as returning <literal>SETOF
+ <replaceable>sometype</></literal>, the function's final
<command>SELECT</> query is executed to completion, and each row it
- outputs is returned as an element of the set.
+ outputs is returned as an element of the result set.
</para>
<para>
- This feature is normally used by calling the function as a table
- function. In this case each row returned by the function becomes
+ This feature is normally used when calling the function in the <literal>FROM</>
+ clause. In this case each row returned by the function becomes
a row of the table seen by the query. For example, assume that
table <literal>foo</> has the same contents as above, and we say:
<programlisting>
-CREATE FUNCTION getfoo(int) RETURNS setof foo AS '
+CREATE FUNCTION getfoo(int) RETURNS SETOF foo AS '
SELECT * FROM foo WHERE fooid = $1;
' LANGUAGE SQL;
SELECT * FROM getfoo(1) AS t1;
</programlisting>
+ Then we would get:
<screen>
fooid | foosubid | fooname
-------+----------+---------
@@ -471,21 +460,19 @@ SELECT * FROM getfoo(1) AS t1;
</para>
<para>
- Currently, functions returning sets may also be called in the target list
- of a <command>SELECT</> query. For each row that the <command>SELECT</>
+ Currently, functions returning sets may also be called in the select list
+ of a query. For each row that the query
generates by itself, the function returning set is invoked, and an output
row is generated for each element of the function's result set. Note,
however, that this capability is deprecated and may be removed in future
releases. The following is an example function returning a set from the
- target list:
+ select list:
-<programlisting>
+<screen>
CREATE FUNCTION listchildren(text) RETURNS SETOF text AS
'SELECT name FROM nodes WHERE parent = $1'
LANGUAGE SQL;
-</programlisting>
-<screen>
SELECT * FROM nodes;
name | parent
-----------+--------
@@ -519,7 +506,7 @@ SELECT name, listchildren(name) FROM nodes;
In the last <command>SELECT</command>,
notice that no output row appears for <literal>Child2</>, <literal>Child3</>, etc.
This happens because <function>listchildren</function> returns an empty set
- for those inputs, so no output rows are generated.
+ for those arguments, so no result rows are generated.
</para>
</sect2>
</sect1>
@@ -562,7 +549,7 @@ SELECT name, listchildren(name) FROM nodes;
<para>
Normally, all internal functions present in the
- backend are declared during the initialization of the database cluster (<command>initdb</command>),
+ server are declared during the initialization of the database cluster (<command>initdb</command>),
but a user could use <command>CREATE FUNCTION</command>
to create additional alias names for an internal function.
Internal functions are declared in <command>CREATE FUNCTION</command>
@@ -571,8 +558,8 @@ SELECT name, listchildren(name) FROM nodes;
<programlisting>
CREATE FUNCTION square_root(double precision) RETURNS double precision
AS 'dsqrt'
- LANGUAGE INTERNAL
- WITH (isStrict);
+ LANGUAGE internal
+ STRICT;
</programlisting>
(Most internal functions expect to be declared <quote>strict</quote>.)
</para>
@@ -587,7 +574,7 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
</sect1>
<sect1 id="xfunc-c">
- <title>C Language Functions</title>
+ <title>C-Language Functions</title>
<para>
User-defined functions can be written in C (or a language that can
@@ -617,7 +604,7 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
<para>
The first time a user-defined function in a particular
- loadable object file is called in a backend session,
+ loadable object file is called in a session,
the dynamic loader loads that object file into memory so that the
function can be called. The <command>CREATE FUNCTION</command>
for a user-defined C function must therefore specify two pieces of
@@ -736,199 +723,19 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
<title>Base Types in C-Language Functions</title>
<para>
- <xref linkend="xfunc-c-type-table"> gives the C type required for
- parameters in the C functions that will be loaded into
- <productname>PostgreSQL</>.
- The <quote>Defined In</quote> column gives the header file that
- needs to be included to get the type definition. (The actual
- definition may be in a different file that is included by the
- listed file. It is recommended that users stick to the defined
- interface.) Note that you should always include
- <filename>postgres.h</filename> first in any source file, because
- it declares a number of things that you will need anyway.
- </para>
-
- <table tocentry="1" id="xfunc-c-type-table">
- <title>Equivalent C Types
- for Built-In <productname>PostgreSQL</productname> Types</title>
- <titleabbrev>Equivalent C Types</titleabbrev>
- <tgroup cols="3">
- <thead>
- <row>
- <entry>
- SQL Type
- </entry>
- <entry>
- C Type
- </entry>
- <entry>
- Defined In
- </entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry><type>abstime</type></entry>
- <entry><type>AbsoluteTime</type></entry>
- <entry><filename>utils/nabstime.h</filename></entry>
- </row>
- <row>
- <entry><type>boolean</type></entry>
- <entry><type>bool</type></entry>
- <entry><filename>postgres.h</filename> (maybe compiler built-in)</entry>
- </row>
- <row>
- <entry><type>box</type></entry>
- <entry><type>BOX*</type></entry>
- <entry><filename>utils/geo_decls.h</filename></entry>
- </row>
- <row>
- <entry><type>bytea</type></entry>
- <entry><type>bytea*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>"char"</type></entry>
- <entry><type>char</type></entry>
- <entry>(compiler built-in)</entry>
- </row>
- <row>
- <entry><type>character</type></entry>
- <entry><type>BpChar*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>cid</type></entry>
- <entry><type>CommandId</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>date</type></entry>
- <entry><type>DateADT</type></entry>
- <entry><filename>utils/date.h</filename></entry>
- </row>
- <row>
- <entry><type>smallint</type> (<type>int2</type>)</entry>
- <entry><type>int2</type> or <type>int16</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>int2vector</type></entry>
- <entry><type>int2vector*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>integer</type> (<type>int4</type>)</entry>
- <entry><type>int4</type> or <type>int32</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>real</type> (<type>float4</type>)</entry>
- <entry><type>float4*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>double precision</type> (<type>float8</type>)</entry>
- <entry><type>float8*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>interval</type></entry>
- <entry><type>Interval*</type></entry>
- <entry><filename>utils/timestamp.h</filename></entry>
- </row>
- <row>
- <entry><type>lseg</type></entry>
- <entry><type>LSEG*</type></entry>
- <entry><filename>utils/geo_decls.h</filename></entry>
- </row>
- <row>
- <entry><type>name</type></entry>
- <entry><type>Name</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>oid</type></entry>
- <entry><type>Oid</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>oidvector</type></entry>
- <entry><type>oidvector*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>path</type></entry>
- <entry><type>PATH*</type></entry>
- <entry><filename>utils/geo_decls.h</filename></entry>
- </row>
- <row>
- <entry><type>point</type></entry>
- <entry><type>POINT*</type></entry>
- <entry><filename>utils/geo_decls.h</filename></entry>
- </row>
- <row>
- <entry><type>regproc</type></entry>
- <entry><type>regproc</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>reltime</type></entry>
- <entry><type>RelativeTime</type></entry>
- <entry><filename>utils/nabstime.h</filename></entry>
- </row>
- <row>
- <entry><type>text</type></entry>
- <entry><type>text*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>tid</type></entry>
- <entry><type>ItemPointer</type></entry>
- <entry><filename>storage/itemptr.h</filename></entry>
- </row>
- <row>
- <entry><type>time</type></entry>
- <entry><type>TimeADT</type></entry>
- <entry><filename>utils/date.h</filename></entry>
- </row>
- <row>
- <entry><type>time with time zone</type></entry>
- <entry><type>TimeTzADT</type></entry>
- <entry><filename>utils/date.h</filename></entry>
- </row>
- <row>
- <entry><type>timestamp</type></entry>
- <entry><type>Timestamp*</type></entry>
- <entry><filename>utils/timestamp.h</filename></entry>
- </row>
- <row>
- <entry><type>tinterval</type></entry>
- <entry><type>TimeInterval</type></entry>
- <entry><filename>utils/nabstime.h</filename></entry>
- </row>
- <row>
- <entry><type>varchar</type></entry>
- <entry><type>VarChar*</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- <row>
- <entry><type>xid</type></entry>
- <entry><type>TransactionId</type></entry>
- <entry><filename>postgres.h</filename></entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <para>
+ To know how to write C-language functions, you need to know how
+ PostgreSQL internally represents base data types and how they can
+ be passed to and from functions.
Internally, <productname>PostgreSQL</productname> regards a
- base type as a <quote>blob of memory</quote>. The user-defined
+ base type as a <quote>blob of memory</quote>. The user-defined
functions that you define over a type in turn define the
way that <productname>PostgreSQL</productname> can operate
on it. That is, <productname>PostgreSQL</productname> will
only store and retrieve the data from disk and use your
user-defined functions to input, process, and output the data.
+ </para>
+
+ <para>
Base types can have one of three internal formats:
<itemizedlist>
@@ -951,7 +758,7 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
</para>
<para>
- By-value types can only be 1, 2 or 4 bytes in length
+ By-value types can only be 1, 2, or 4 bytes in length
(also 8 bytes, if <literal>sizeof(Datum)</literal> is 8 on your machine).
You should be careful
to define your types such that they will be the same
@@ -967,10 +774,6 @@ CREATE FUNCTION square_root(double precision) RETURNS double precision
/* 4-byte integer, passed by value */
typedef int int4;
</programlisting>
-
- <productname>PostgreSQL</productname> automatically figures
- things out so that the integer types really have the size they
- advertise.
</para>
<para>
@@ -985,16 +788,15 @@ typedef struct
double x, y;
} Point;
</programlisting>
- </para>
- <para>
Only pointers to such types can be used when passing
them in and out of <productname>PostgreSQL</productname> functions.
To return a value of such a type, allocate the right amount of
- memory with <literal>palloc()</literal>, fill in the allocated memory,
- and return a pointer to it. (Alternatively, you can return an input
- value of the same type by returning its pointer. <emphasis>Never</>
- modify the contents of a pass-by-reference input value, however.)
+ memory with <literal>palloc</literal>, fill in the allocated memory,
+ and return a pointer to it. (You can also return an input value
+ that has the same type as the return value directly by returning
+ the pointer to the input value. <emphasis>Never</> modify the
+ contents of a pass-by-reference input value, however.)
</para>
<para>
@@ -1003,9 +805,14 @@ typedef struct
with a length field of exactly 4 bytes, and all data to
be stored within that type must be located in the memory
immediately following that length field. The
- length field is the total length of the structure
- (i.e., it includes the size of the length field
- itself). We can define the text type as follows:
+ length field contains the total length of the structure,
+ that is, it includes the size of the length field
+ itself.
+ </para>
+
+ <para>
+ As an example, we can define the type <type>text</type> as
+ follows:
<programlisting>
typedef struct {
@@ -1013,22 +820,21 @@ typedef struct {
char data[1];
} text;
</programlisting>
- </para>
- <para>
Obviously, the data field declared here is not long enough to hold
all possible strings. Since it's impossible to declare a variable-size
structure in <acronym>C</acronym>, we rely on the knowledge that the
<acronym>C</acronym> compiler won't range-check array subscripts. We
just allocate the necessary amount of space and then access the array as
- if it were declared the right length. (If this isn't a familiar trick to
- you, you may wish to spend some time with an introductory
- <acronym>C</acronym> programming textbook before delving deeper into
- <productname>PostgreSQL</productname> server programming.)
+ if it were declared the right length. (This is a common trick, which
+ you can read about in many textbooks about C.)
+ </para>
+
+ <para>
When manipulating
variable-length types, we must be careful to allocate
the correct amount of memory and set the length field correctly.
- For example, if we wanted to store 40 bytes in a text
+ For example, if we wanted to store 40 bytes in a <structname>text</>
structure, we might use a code fragment like this:
<programlisting>
@@ -1047,6 +853,190 @@ memcpy(destination->data, buffer, 40);
to refer to the size of the overhead for a variable-length type.
</para>
+ <para>
+ <xref linkend="xfunc-c-type-table"> specifies which C type
+ corresponds to which SQL type when writing a C-language function
+ that uses a built-in type of <productname>PostgreSQL</>.
+ The <quote>Defined In</quote> column gives the header file that
+ needs to be included to get the type definition. (The actual
+ definition may be in a different file that is included by the
+ listed file. It is recommended that users stick to the defined
+ interface.) Note that you should always include
+ <filename>postgres.h</filename> first in any source file, because
+ it declares a number of things that you will need anyway.
+ </para>
+
+ <table tocentry="1" id="xfunc-c-type-table">
+ <title>Equivalent C Types for Built-In SQL Types</title>
+ <tgroup cols="3">
+ <thead>
+ <row>
+ <entry>
+ SQL Type
+ </entry>
+ <entry>
+ C Type
+ </entry>
+ <entry>
+ Defined In
+ </entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><type>abstime</type></entry>
+ <entry><type>AbsoluteTime</type></entry>
+ <entry><filename>utils/nabstime.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>boolean</type></entry>
+ <entry><type>bool</type></entry>
+ <entry><filename>postgres.h</filename> (maybe compiler built-in)</entry>
+ </row>
+ <row>
+ <entry><type>box</type></entry>
+ <entry><type>BOX*</type></entry>
+ <entry><filename>utils/geo_decls.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>bytea</type></entry>
+ <entry><type>bytea*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>"char"</type></entry>
+ <entry><type>char</type></entry>
+ <entry>(compiler built-in)</entry>
+ </row>
+ <row>
+ <entry><type>character</type></entry>
+ <entry><type>BpChar*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>cid</type></entry>
+ <entry><type>CommandId</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>date</type></entry>
+ <entry><type>DateADT</type></entry>
+ <entry><filename>utils/date.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>smallint</type> (<type>int2</type>)</entry>
+ <entry><type>int2</type> or <type>int16</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>int2vector</type></entry>
+ <entry><type>int2vector*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>integer</type> (<type>int4</type>)</entry>
+ <entry><type>int4</type> or <type>int32</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>real</type> (<type>float4</type>)</entry>
+ <entry><type>float4*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>double precision</type> (<type>float8</type>)</entry>
+ <entry><type>float8*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>interval</type></entry>
+ <entry><type>Interval*</type></entry>
+ <entry><filename>utils/timestamp.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>lseg</type></entry>
+ <entry><type>LSEG*</type></entry>
+ <entry><filename>utils/geo_decls.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>name</type></entry>
+ <entry><type>Name</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>oid</type></entry>
+ <entry><type>Oid</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>oidvector</type></entry>
+ <entry><type>oidvector*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>path</type></entry>
+ <entry><type>PATH*</type></entry>
+ <entry><filename>utils/geo_decls.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>point</type></entry>
+ <entry><type>POINT*</type></entry>
+ <entry><filename>utils/geo_decls.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>regproc</type></entry>
+ <entry><type>regproc</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>reltime</type></entry>
+ <entry><type>RelativeTime</type></entry>
+ <entry><filename>utils/nabstime.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>text</type></entry>
+ <entry><type>text*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>tid</type></entry>
+ <entry><type>ItemPointer</type></entry>
+ <entry><filename>storage/itemptr.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>time</type></entry>
+ <entry><type>TimeADT</type></entry>
+ <entry><filename>utils/date.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>time with time zone</type></entry>
+ <entry><type>TimeTzADT</type></entry>
+ <entry><filename>utils/date.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>timestamp</type></entry>
+ <entry><type>Timestamp*</type></entry>
+ <entry><filename>utils/timestamp.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>tinterval</type></entry>
+ <entry><type>TimeInterval</type></entry>
+ <entry><filename>utils/nabstime.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>varchar</type></entry>
+ <entry><type>VarChar*</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ <row>
+ <entry><type>xid</type></entry>
+ <entry><type>TransactionId</type></entry>
+ <entry><filename>postgres.h</filename></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
<para>
Now that we've gone over all of the possible structures
for base types, we can show some examples of real functions.
@@ -1054,7 +1044,7 @@ memcpy(destination->data, buffer, 40);
</sect2>
<sect2>
- <title>Version-0 Calling Conventions for C-Language Functions</title>
+ <title>Calling Conventions Version 0 for C-Language Functions</title>
<para>
We present the <quote>old style</quote> calling convention first --- although
@@ -1072,7 +1062,7 @@ memcpy(destination->data, buffer, 40);
#include "postgres.h"
#include <string.h>
-/* By Value */
+/* by value */
int
add_one(int arg)
@@ -1080,7 +1070,7 @@ add_one(int arg)
return arg + 1;
}
-/* By Reference, Fixed Length */
+/* by reference, fixed length */
float8 *
add_one_float8(float8 *arg)
@@ -1103,7 +1093,7 @@ makepoint(Point *pointx, Point *pointy)
return new_point;
}
-/* By Reference, Variable Length */
+/* by reference, variable length */
text *
copytext(text *t)
@@ -1144,47 +1134,48 @@ concat_text(text *arg1, text *arg2)
with commands like this:
<programlisting>
-CREATE FUNCTION add_one(int4) RETURNS int4
- AS '<replaceable>PGROOT</replaceable>/tutorial/funcs' LANGUAGE C
- WITH (isStrict);
+CREATE FUNCTION add_one(integer) RETURNS integer
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'add_one'
+ LANGUAGE C STRICT;
--- note overloading of SQL function name add_one()
-CREATE FUNCTION add_one(float8) RETURNS float8
- AS '<replaceable>PGROOT</replaceable>/tutorial/funcs',
- 'add_one_float8'
- LANGUAGE C WITH (isStrict);
+-- note overloading of SQL function name "add_one"
+CREATE FUNCTION add_one(double precision) RETURNS double precision
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'add_one_float8'
+ LANGUAGE C STRICT;
CREATE FUNCTION makepoint(point, point) RETURNS point
- AS '<replaceable>PGROOT</replaceable>/tutorial/funcs' LANGUAGE C
- WITH (isStrict);
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'makepoint'
+ LANGUAGE C STRICT;
CREATE FUNCTION copytext(text) RETURNS text
- AS '<replaceable>PGROOT</replaceable>/tutorial/funcs' LANGUAGE C
- WITH (isStrict);
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'copytext'
+ LANGUAGE C STRICT;
CREATE FUNCTION concat_text(text, text) RETURNS text
- AS '<replaceable>PGROOT</replaceable>/tutorial/funcs' LANGUAGE C
- WITH (isStrict);
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'concat_text',
+ LANGUAGE C STRICT;
</programlisting>
</para>
<para>
- Here <replaceable>PGROOT</replaceable> stands for the full path to
- the <productname>PostgreSQL</productname> source tree. (Better style would
- be to use just <literal>'funcs'</> in the <literal>AS</> clause,
- after having added <replaceable>PGROOT</replaceable><literal>/tutorial</>
- to the search path. In any case, we may omit the system-specific
- extension for a shared library, commonly <literal>.so</literal> or
+ Here, <replaceable>DIRECTORY</replaceable> stands for the
+ directory of the shared library file (for instance the PostgreSQL
+ tutorial directory, which contains the code for the examples used
+ in this section). (Better style would be to use just
+ <literal>'funcs'</> in the <literal>AS</> clause, after having
+ added <replaceable>DIRECTORY</replaceable> to the search path.
+ In any case, we may omit the system-specific extension for a
+ shared library, commonly <literal>.so</literal> or
<literal>.sl</literal>.)
</para>
<para>
Notice that we have specified the functions as <quote>strict</quote>,
meaning that
- the system should automatically assume a NULL result if any input
- value is NULL. By doing this, we avoid having to check for NULL inputs
+ the system should automatically assume a null result if any input
+ value is null. By doing this, we avoid having to check for null inputs
in the function code. Without this, we'd have to check for null values
- explicitly, for example by checking for a null pointer for each
+ explicitly, by checking for a null pointer for each
pass-by-reference argument. (For pass-by-value arguments, we don't
even have a way to check!)
</para>
@@ -1192,15 +1183,15 @@ CREATE FUNCTION concat_text(text, text) RETURNS text
<para>
Although this calling convention is simple to use,
it is not very portable; on some architectures there are problems
- with passing smaller-than-int data types this way. Also, there is
- no simple way to return a NULL result, nor to cope with NULL arguments
+ with passing data types that are smaller than <type>int</type> this way. Also, there is
+ no simple way to return a null result, nor to cope with null arguments
in any way other than making the function strict. The version-1
convention, presented next, overcomes these objections.
</para>
</sect2>
<sect2>
- <title>Version-1 Calling Conventions for C-Language Functions</title>
+ <title>Calling Conventions Version 1 for C-Language Functions</title>
<para>
The version-1 calling convention relies on macros to suppress most
@@ -1213,21 +1204,26 @@ Datum funcname(PG_FUNCTION_ARGS)
<programlisting>
PG_FUNCTION_INFO_V1(funcname);
</programlisting>
- must appear in the same source file (conventionally it's written
- just before the function itself). This macro call is not needed
- for <literal>internal</>-language functions, since
- <productname>PostgreSQL</> currently
- assumes all internal functions are version-1. However, it is
- <emphasis>required</emphasis> for dynamically-loaded functions.
+ must appear in the same source file. (Conventionally. it's
+ written just before the function itself.) This macro call is not
+ needed for <literal>internal</>-language functions, since
+ <productname>PostgreSQL</> assumes that all internal functions
+ use the version-1 convention. It is, however, required for
+ dynamically-loaded functions.
</para>
<para>
In a version-1 function, each actual argument is fetched using a
<function>PG_GETARG_<replaceable>xxx</replaceable>()</function>
- macro that corresponds to the argument's data type, and the result
- is returned using a
+ macro that corresponds to the argument's data type, and the
+ result is returned using a
<function>PG_RETURN_<replaceable>xxx</replaceable>()</function>
macro for the return type.
+ <function>PG_GETARG_<replaceable>xxx</replaceable>()</function>
+ takes as its argument the number of the function argument to
+ fetch, where the count starts at 0.
+ <function>PG_RETURN_<replaceable>xxx</replaceable>()</function>
+ takes as its argument the actual value to return.
</para>
<para>
@@ -1238,7 +1234,7 @@ PG_FUNCTION_INFO_V1(funcname);
#include <string.h>
#include "fmgr.h"
-/* By Value */
+/* by value */
PG_FUNCTION_INFO_V1(add_one);
@@ -1250,14 +1246,14 @@ add_one(PG_FUNCTION_ARGS)
PG_RETURN_INT32(arg + 1);
}
-/* By Reference, Fixed Length */
+/* b reference, fixed length */
PG_FUNCTION_INFO_V1(add_one_float8);
Datum
add_one_float8(PG_FUNCTION_ARGS)
{
- /* The macros for FLOAT8 hide its pass-by-reference nature */
+ /* The macros for FLOAT8 hide its pass-by-reference nature. */
float8 arg = PG_GETARG_FLOAT8(0);
PG_RETURN_FLOAT8(arg + 1.0);
@@ -1268,7 +1264,7 @@ PG_FUNCTION_INFO_V1(makepoint);
Datum
makepoint(PG_FUNCTION_ARGS)
{
- /* Here, the pass-by-reference nature of Point is not hidden */
+ /* Here, the pass-by-reference nature of Point is not hidden. */
Point *pointx = PG_GETARG_POINT_P(0);
Point *pointy = PG_GETARG_POINT_P(1);
Point *new_point = (Point *) palloc(sizeof(Point));
@@ -1279,7 +1275,7 @@ makepoint(PG_FUNCTION_ARGS)
PG_RETURN_POINT_P(new_point);
}
-/* By Reference, Variable Length */
+/* by reference, variable length */
PG_FUNCTION_INFO_V1(copytext);
@@ -1327,80 +1323,178 @@ concat_text(PG_FUNCTION_ARGS)
<para>
At first glance, the version-1 coding conventions may appear to
- be just pointless obscurantism. However, they do offer a number
+ be just pointless obscurantism. They do, however, offer a number
of improvements, because the macros can hide unnecessary detail.
An example is that in coding <function>add_one_float8</>, we no longer need to
be aware that <type>float8</type> is a pass-by-reference type. Another
- example is that the <literal>GETARG</> macros for variable-length types hide
- the need to deal with fetching <quote>toasted</quote> (compressed or
- out-of-line) values. The old-style <function>copytext</function>
- and <function>concat_text</function> functions shown above are
- actually wrong in the presence of toasted values, because they
- don't call <function>pg_detoast_datum()</function> on their
- inputs. (The handler for old-style dynamically-loaded functions
- currently takes care of this detail, but it does so less
- efficiently than is possible for a version-1 function.)
+ example is that the <literal>GETARG</> macros for variable-length types allow
+ for more efficient fetching of <quote>toasted</quote> (compressed or
+ out-of-line) values.
</para>
<para>
- One big improvement in version-1 functions is better handling of NULL
+ One big improvement in version-1 functions is better handling of null
inputs and results. The macro <function>PG_ARGISNULL(<replaceable>n</>)</function>
- allows a function to test whether each input is NULL (of course, doing
- this is only necessary in functions not declared <quote>strict</>).
+ allows a function to test whether each input is null. (Of course, doing
+ this is only necessary in functions not declared <quote>strict</>.)
As with the
<function>PG_GETARG_<replaceable>xxx</replaceable>()</function> macros,
the input arguments are counted beginning at zero. Note that one
should refrain from executing
<function>PG_GETARG_<replaceable>xxx</replaceable>()</function> until
- one has verified that the argument isn't NULL.
- To return a NULL result, execute <function>PG_RETURN_NULL()</function>;
+ one has verified that the argument isn't null.
+ To return a null result, execute <function>PG_RETURN_NULL()</function>;
this works in both strict and nonstrict functions.
</para>
<para>
- Other options provided in the new-style interface are two
+ Other options provided in the new-style interface are two
variants of the
<function>PG_GETARG_<replaceable>xxx</replaceable>()</function>
macros. The first of these,
- <function>PG_GETARG_<replaceable>xxx</replaceable>_COPY()</function>
- guarantees to return a copy of the specified parameter which is
+ <function>PG_GETARG_<replaceable>xxx</replaceable>_COPY()</function>,
+ guarantees to return a copy of the specified argument that is
safe for writing into. (The normal macros will sometimes return a
- pointer to a value that is physically stored in a table, and so
+ pointer to a value that is physically stored in a table, which
must not be written to. Using the
<function>PG_GETARG_<replaceable>xxx</replaceable>_COPY()</function>
macros guarantees a writable result.)
- </para>
-
- <para>
The second variant consists of the
<function>PG_GETARG_<replaceable>xxx</replaceable>_SLICE()</function>
- macros which take three parameters. The first is the number of the
- parameter (as above). The second and third are the offset and
+ macros which take three arguments. The first is the number of the
+ function argument (as above). The second and third are the offset and
length of the segment to be returned. Offsets are counted from
zero, and a negative length requests that the remainder of the
- value be returned. These routines provide more efficient access to
+ value be returned. These macros provide more efficient access to
parts of large values in the case where they have storage type
<quote>external</quote>. (The storage type of a column can be specified using
<literal>ALTER TABLE <replaceable>tablename</replaceable> ALTER
COLUMN <replaceable>colname</replaceable> SET STORAGE
- <replaceable>storagetype</replaceable></literal>. Storage type is one of
+ <replaceable>storagetype</replaceable></literal>. <replaceable>storagetype</replaceable> is one of
<literal>plain</>, <literal>external</>, <literal>extended</literal>,
or <literal>main</>.)
</para>
<para>
- The version-1 function call conventions make it possible to
- return <quote>set</quote> results and implement trigger functions and
- procedural-language call handlers. Version-1 code is also more
- portable than version-0, because it does not break ANSI C restrictions
- on function call protocol. For more details see
- <filename>src/backend/utils/fmgr/README</filename> in the source
- distribution.
+ Finally, the version-1 function call conventions make it possible
+ to return set results (<xref linkend="xfunc-c-return-set">) and
+ implement trigger functions (<xref linkend="triggers">) and
+ procedural-language call handlers (<xref
+ linkend="xfunc-plhandler">). Version-1 code is also more
+ portable than version-0, because it does not break restrictions
+ on function call protocol in the C standard. For more details
+ see <filename>src/backend/utils/fmgr/README</filename> in the
+ source distribution.
+ </para>
+ </sect2>
+
+ <sect2>
+ <title>Writing Code</title>
+
+ <para>
+ Before we turn to the more advanced topics, we should discuss
+ some coding rules for PostgreSQL C-language functions. While it
+ may be possible to load functions written in languages other than
+ C into <productname>PostgreSQL</productname>, this is usually
+ difficult (when it is possible at all) because other languages,
+ such as C++, FORTRAN, or Pascal often do not follow the same
+ calling convention as C. That is, other languages do not pass
+ argument and return values between functions in the same way.
+ For this reason, we will assume that your C-language functions
+ are actually written in C.
+ </para>
+
+ <para>
+ The basic rules for writing and building C functions are as follows:
+
+ <itemizedlist>
+ <listitem>
+ <para>
+ Use <literal>pg_config
+ --includedir-server</literal><indexterm><primary>pg_config</></>
+ to find out where the <productname>PostgreSQL</> server header
+ files are installed on your system (or the system that your
+ users will be running on). This option is new with
+ <productname>PostgreSQL</> 7.2. For
+ <productname>PostgreSQL</> 7.1 you should use the option
+ <option>--includedir</option>. (<command>pg_config</command>
+ will exit with a non-zero status if it encounters an unknown
+ option.) For releases prior to 7.1 you will have to guess,
+ but since that was before the current calling conventions were
+ introduced, it is unlikely that you want to support those
+ releases.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ When allocating memory, use the
+ <productname>PostgreSQL</productname> functions
+ <function>palloc</function> and <function>pfree</function>
+ instead of the corresponding C library functions
+ <function>malloc</function> and <function>free</function>.
+ The memory allocated by <function>palloc</function> will be
+ freed automatically at the end of each transaction, preventing
+ memory leaks.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Always zero the bytes of your structures using
+ <function>memset</function> or <function>bzero</function>.
+ Several routines (such as the hash access method, hash joins,
+ and the sort algorithm) compute functions of the raw bits
+ contained in your structure. Even if you initialize all
+ fields of your structure, there may be several bytes of
+ alignment padding (holes in the structure) that may contain
+ garbage values.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Most of the internal <productname>PostgreSQL</productname>
+ types are declared in <filename>postgres.h</filename>, while
+ the function manager interfaces
+ (<symbol>PG_FUNCTION_ARGS</symbol>, etc.) are in
+ <filename>fmgr.h</filename>, so you will need to include at
+ least these two files. For portability reasons it's best to
+ include <filename>postgres.h</filename> <emphasis>first</>,
+ before any other system or user header files. Including
+ <filename>postgres.h</filename> will also include
+ <filename>elog.h</filename> and <filename>palloc.h</filename>
+ for you.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Symbol names defined within object files must not conflict
+ with each other or with symbols defined in the
+ <productname>PostgreSQL</productname> server executable. You
+ will have to rename your functions or variables if you get
+ error messages to this effect.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Compiling and linking your code so that it can be dynamically
+ loaded into <productname>PostgreSQL</productname> always
+ requires special flags. See <xref linkend="dfunc"> for a
+ detailed explanation of how to do it for your particular
+ operating system.
+ </para>
+ </listitem>
+ </itemizedlist>
</para>
</sect2>
+&dfunc;
+
<sect2>
- <title>Composite Types in C-Language Functions</title>
+ <title>Composite-Type Arguments in C-Language Functions</title>
<para>
Composite types do not have a fixed layout like C
@@ -1409,26 +1503,28 @@ concat_text(PG_FUNCTION_ARGS)
part of an inheritance hierarchy may have different
fields than other members of the same inheritance hierarchy.
Therefore, <productname>PostgreSQL</productname> provides
- a procedural interface for accessing fields of composite types
- from C. As <productname>PostgreSQL</productname> processes
- a set of rows, each row will be passed into your
- function as an opaque structure of type <literal>TUPLE</literal>.
+ a function interface for accessing fields of composite types
+ from C.
+ </para>
+
+ <para>
Suppose we want to write a function to answer the query
<programlisting>
SELECT name, c_overpaid(emp, 1500) AS overpaid
-FROM emp
-WHERE name = 'Bill' OR name = 'Sam';
+ FROM emp
+ WHERE name = 'Bill' OR name = 'Sam';
</programlisting>
- In the query above, we can define <function>c_overpaid</> as:
+ Using call conventions version 0, we can define
+ <function>c_overpaid</> as:
<programlisting>
#include "postgres.h"
#include "executor/executor.h" /* for GetAttributeByName() */
bool
-c_overpaid(TupleTableSlot *t, /* the current row of EMP */
+c_overpaid(TupleTableSlot *t, /* the current row of emp */
int32 limit)
{
bool isnull;
@@ -1436,11 +1532,16 @@ c_overpaid(TupleTableSlot *t, /* the current row of EMP */
salary = DatumGetInt32(GetAttributeByName(t, "salary", &isnull));
if (isnull)
- return (false);
+ return false;
return salary > limit;
}
+</programlisting>
+
+ In version-1 coding, the above would look like this:
-/* In version-1 coding, the above would look like this: */
+<programlisting>
+#include "postgres.h"
+#include "executor/executor.h" /* for GetAttributeByName() */
PG_FUNCTION_INFO_V1(c_overpaid);
@@ -1455,7 +1556,7 @@ c_overpaid(PG_FUNCTION_ARGS)
salary = DatumGetInt32(GetAttributeByName(t, "salary", &isnull));
if (isnull)
PG_RETURN_BOOL(false);
- /* Alternatively, we might prefer to do PG_RETURN_NULL() for null salary */
+ /* Alternatively, we might prefer to do PG_RETURN_NULL() for null salary. */
PG_RETURN_BOOL(salary > limit);
}
@@ -1465,7 +1566,7 @@ c_overpaid(PG_FUNCTION_ARGS)
<para>
<function>GetAttributeByName</function> is the
<productname>PostgreSQL</productname> system function that
- returns attributes out of the current row. It has
+ returns attributes out of the specified row. It has
three arguments: the argument of type <type>TupleTableSlot*</type> passed into
the function, the name of the desired attribute, and a
return parameter that tells whether the attribute
@@ -1475,55 +1576,43 @@ c_overpaid(PG_FUNCTION_ARGS)
</para>
<para>
- The following command lets <productname>PostgreSQL</productname>
- know about the <function>c_overpaid</function> function:
+ The following command declares the function
+ <function>c_overpaid</function> in SQL:
<programlisting>
-CREATE FUNCTION c_overpaid(emp, int4)
-RETURNS bool
-AS '<replaceable>PGROOT</replaceable>/tutorial/funcs'
-LANGUAGE C;
+CREATE FUNCTION c_overpaid(emp, integer)
+ RETURNS boolean
+ AS '<replaceable>DIRECTORY</replaceable>/funcs', 'c_overpaid'
+ LANGUAGE C;
</programlisting>
</para>
</sect2>
<sect2>
- <title>Table Function API</title>
-
- <para>
- The Table Function API assists in the creation of user-defined
- C language table functions (<xref linkend="xfunc-tablefunctions">).
- Table functions are functions that produce a set of rows, made up of
- either base (scalar) data types, or composite (multi-column) data types.
- The API is split into two main components: support for returning
- composite data types, and support for returning multiple rows
- (set-returning functions or <acronym>SRF</>s).
- </para>
+ <title>Returning Rows (Composite Types) from C-Language Functions</title>
<para>
- The Table Function API relies on macros and functions to suppress most
- of the complexity of building composite data types and returning multiple
- results. A table function must follow the version-1 calling convention
- described above. In addition, the source file must include:
+ To return a row or composite-type value from a C-language
+ function, you can use a special API that provides macros and
+ functions to hide most of the complexity of building composite
+ data types. To use this API, the source file must include:
<programlisting>
#include "funcapi.h"
</programlisting>
</para>
- <sect3>
- <title>Returning Rows (Composite Types)</title>
-
<para>
- The Table Function API support for returning composite data types
- (or rows) starts with the <structname>AttInMetadata</>
- structure. This structure holds arrays of individual attribute
- information needed to create a row from raw C strings. It also
- saves a pointer to the <structname>TupleDesc</>. The information
- carried here is derived from the <structname>TupleDesc</>, but it
- is stored here to avoid redundant CPU cycles on each call to a
- table function. In the case of a function returning a set, the
- <structname>AttInMetadata</> structure should be computed
- once during the first call and saved for re-use in later calls.
+ The support for returning composite data types (or rows) starts
+ with the <structname>AttInMetadata</> structure. This structure
+ holds arrays of individual attribute information needed to create
+ a row from raw C strings. The information contained in the
+ structure is derived from a <structname>TupleDesc</> structure,
+ but it is stored to avoid redundant computations on each call to
+ a set-returning function (see next section). In the case of a
+ function returning a set, the <structname>AttInMetadata</>
+ structure should be computed once during the first call and saved
+ for reuse in later calls. <structname>AttInMetadata</> also
+ saves a pointer to the original <structname>TupleDesc</>.
<programlisting>
typedef struct AttInMetadata
{
@@ -1548,13 +1637,13 @@ typedef struct AttInMetadata
<programlisting>
TupleDesc RelationNameGetTupleDesc(const char *relname)
</programlisting>
- to get a <structname>TupleDesc</> based on a specified relation, or
+ to get a <structname>TupleDesc</> for a named relation, or
<programlisting>
TupleDesc TypeGetTupleDesc(Oid typeoid, List *colaliases)
</programlisting>
to get a <structname>TupleDesc</> based on a type OID. This can
- be used to get a <structname>TupleDesc</> for a base (scalar) or
- composite (relation) type. Then
+ be used to get a <structname>TupleDesc</> for a base or
+ composite type. Then
<programlisting>
AttInMetadata *TupleDescGetAttInMetadata(TupleDesc tupdesc)
</programlisting>
@@ -1562,8 +1651,7 @@ AttInMetadata *TupleDescGetAttInMetadata(TupleDesc tupdesc)
initialized based on the given
<structname>TupleDesc</>. <structname>AttInMetadata</> can be
used in conjunction with C strings to produce a properly formed
- tuple. The metadata is stored here to avoid redundant work across
- multiple calls.
+ row value (internally called tuple).
</para>
<para>
@@ -1574,7 +1662,7 @@ TupleTableSlot *TupleDescGetSlot(TupleDesc tupdesc)
</programlisting>
to initialize this tuple slot, or obtain one through other (user provided)
means. The tuple slot is needed to create a <type>Datum</> for return by the
- function. The same slot can (and should) be re-used on each call.
+ function. The same slot can (and should) be reused on each call.
</para>
<para>
@@ -1583,13 +1671,13 @@ TupleTableSlot *TupleDescGetSlot(TupleDesc tupdesc)
HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
</programlisting>
can be used to build a <structname>HeapTuple</> given user data
- in C string form. <quote>values</quote> is an array of C strings, one for
- each attribute of the return tuple. Each C string should be in
+ in C string form. <literal>values</literal> is an array of C strings, one for
+ each attribute of the return row. Each C string should be in
the form expected by the input function of the attribute data
type. In order to return a null value for one of the attributes,
the corresponding pointer in the <parameter>values</> array
should be set to <symbol>NULL</>. This function will need to
- be called again for each tuple you return.
+ be called again for each row you return.
</para>
<para>
@@ -1597,16 +1685,16 @@ HeapTuple BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
<function>BuildTupleFromCStrings</> is only convenient if your
function naturally computes the values to be returned as text
strings. If your code naturally computes the values as a set of
- Datums, you should instead use the underlying
- <function>heap_formtuple</> routine to convert the
- <type>Datum</type>s directly into a tuple. You will still need
+ <type>Datum</> values, you should instead use the underlying
+ function <function>heap_formtuple</> to convert the
+ <type>Datum</type> values directly into a tuple. You will still need
the <structname>TupleDesc</> and a <structname>TupleTableSlot</>,
but not <structname>AttInMetadata</>.
</para>
<para>
- Once you have built a tuple to return from your function, the tuple must
- be converted into a <type>Datum</>. Use
+ Once you have built a tuple to return from your function, it
+ must be converted into a <type>Datum</>. Use
<programlisting>
TupleGetDatum(TupleTableSlot *slot, HeapTuple tuple)
</programlisting>
@@ -1617,28 +1705,36 @@ TupleGetDatum(TupleTableSlot *slot, HeapTuple tuple)
</para>
<para>
- An example appears below.
+ An example appears in the next section.
</para>
- </sect3>
+ </sect2>
+
+ <sect2 id="xfunc-c-return-set">
+ <title>Returning Sets from C-Language Functions</title>
- <sect3>
- <title>Returning Sets</title>
+ <para>
+ There is also a special API that provides support for returning
+ sets (multiple rows) from a C-language function. A set-returning
+ function must follow the version-1 calling conventions. Also,
+ source files must include <filename>funcapi.h</filename>, as
+ above.
+ </para>
<para>
- A set-returning function (<acronym>SRF</>) is normally called
+ A set-returning function (<acronym>SRF</>) is called
once for each item it returns. The <acronym>SRF</> must
therefore save enough state to remember what it was doing and
- return the next item on each call. The Table Function API
- provides the <structname>FuncCallContext</> structure to help
- control this process. <literal>fcinfo->flinfo->fn_extra</>
+ return the next item on each call.
+ The structure <structname>FuncCallContext</> is provided to help
+ control this process. Within a function, <literal>fcinfo->flinfo->fn_extra</>
is used to hold a pointer to <structname>FuncCallContext</>
across calls.
<programlisting>
typedef struct
{
/*
- * Number of times we've been called before.
+ * Number of times we've been called before
*
* call_cntr is initialized to 0 for you by SRF_FIRSTCALL_INIT(), and
* incremented for you every time SRF_RETURN_NEXT() is called.
@@ -1648,7 +1744,7 @@ typedef struct
/*
* OPTIONAL maximum number of calls
*
- * max_calls is here for convenience ONLY and setting it is OPTIONAL.
+ * max_calls is here for convenience only and setting it is optional.
* If not set, you must provide alternative means to know when the
* function is done.
*/
@@ -1657,41 +1753,43 @@ typedef struct
/*
* OPTIONAL pointer to result slot
*
- * slot is for use when returning tuples (i.e. composite data types)
- * and is not needed when returning base (i.e. scalar) data types.
+ * slot is for use when returning tuples (i.e., composite data types)
+ * and is not needed when returning base data types.
*/
TupleTableSlot *slot;
/*
- * OPTIONAL pointer to misc user provided context info
+ * OPTIONAL pointer to miscellaneous user-provided context information
*
- * user_fctx is for use as a pointer to your own struct to retain
- * arbitrary context information between calls for your function.
+ * user_fctx is for use as a pointer to your own data to retain
+ * arbitrary context information between calls of your function.
*/
void *user_fctx;
/*
- * OPTIONAL pointer to struct containing arrays of attribute type input
- * metainfo
+ * OPTIONAL pointer to struct containing attribute type input metadata
*
- * attinmeta is for use when returning tuples (i.e. composite data types)
- * and is not needed when returning base (i.e. scalar) data types. It
- * is ONLY needed if you intend to use BuildTupleFromCStrings() to create
+ * attinmeta is for use when returning tuples (i.e., composite data types)
+ * and is not needed when returning base data types. It
+ * is only needed if you intend to use BuildTupleFromCStrings() to create
* the return tuple.
*/
AttInMetadata *attinmeta;
/*
- * memory context used for structures which must live for multiple calls
+ * memory context used for structures that must live for multiple calls
*
* multi_call_memory_ctx is set by SRF_FIRSTCALL_INIT() for you, and used
* by SRF_RETURN_DONE() for cleanup. It is the most appropriate memory
- * context for any memory that is to be re-used across multiple calls
+ * context for any memory that is to be reused across multiple calls
* of the SRF.
*/
MemoryContext multi_call_memory_ctx;
} FuncCallContext;
</programlisting>
+ </para>
+
+ <para>
An <acronym>SRF</> uses several functions and macros that
automatically manipulate the <structname>FuncCallContext</>
structure (and expect to find it via <literal>fn_extra</>). Use
@@ -1718,9 +1816,9 @@ SRF_PERCALL_SETUP()
<programlisting>
SRF_RETURN_NEXT(funcctx, result)
</programlisting>
- to return it to the caller. (The <literal>result</> must be a
+ to return it to the caller. (<literal>result</> must be of type
<type>Datum</>, either a single value or a tuple prepared as
- described earlier.) Finally, when your function is finished
+ described above.) Finally, when your function is finished
returning data, use
<programlisting>
SRF_RETURN_DONE(funcctx)
@@ -1731,8 +1829,8 @@ SRF_RETURN_DONE(funcctx)
<para>
The memory context that is current when the <acronym>SRF</> is called is
a transient context that will be cleared between calls. This means
- that you do not need to <function>pfree</> everything
- you <function>palloc</>; it will go away anyway. However, if you want to allocate
+ that you do not need to call <function>pfree</> on everything
+ you allocated using <function>palloc</>; it will go away anyway. However, if you want to allocate
any data structures to live across calls, you need to put them somewhere
else. The memory context referenced by
<structfield>multi_call_memory_ctx</> is a suitable location for any
@@ -1745,45 +1843,45 @@ SRF_RETURN_DONE(funcctx)
A complete pseudo-code example looks like the following:
<programlisting>
Datum
-my_Set_Returning_Function(PG_FUNCTION_ARGS)
+my_set_returning_function(PG_FUNCTION_ARGS)
{
FuncCallContext *funcctx;
Datum result;
MemoryContext oldcontext;
- [user defined declarations]
+ <replaceable>further declarations as needed</replaceable>
if (SRF_IS_FIRSTCALL())
{
funcctx = SRF_FIRSTCALL_INIT();
oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
- /* one-time setup code appears here: */
- [user defined code]
- [if returning composite]
- [build TupleDesc, and perhaps AttInMetadata]
- [obtain slot]
+ /* One-time setup code appears here: */
+ <replaceable>user code</replaceable>
+ <replaceable>if returning composite</replaceable>
+ <replaceable>build TupleDesc, and perhaps AttInMetadata</replaceable>
+ <replaceable>obtain slot</replaceable>
funcctx->slot = slot;
- [endif returning composite]
- [user defined code]
+ <replaceable>endif returning composite</replaceable>
+ <replaceable>user code</replaceable>
MemoryContextSwitchTo(oldcontext);
}
- /* each-time setup code appears here: */
- [user defined code]
+ /* Each-time setup code appears here: */
+ <replaceable>user code</replaceable>
funcctx = SRF_PERCALL_SETUP();
- [user defined code]
+ <replaceable>user code</replaceable>
/* this is just one way we might test whether we are done: */
if (funcctx->call_cntr < funcctx->max_calls)
{
- /* here we want to return another item: */
- [user defined code]
- [obtain result Datum]
+ /* Here we want to return another item: */
+ <replaceable>user code</replaceable>
+ <replaceable>obtain result Datum</replaceable>
SRF_RETURN_NEXT(funcctx, result);
}
else
{
- /* here we are done returning items, and just need to clean up: */
- [user defined code]
+ /* Here we are done returning items and just need to clean up: */
+ <replaceable>user code</replaceable>
SRF_RETURN_DONE(funcctx);
}
}
@@ -1794,6 +1892,7 @@ my_Set_Returning_Function(PG_FUNCTION_ARGS)
A complete example of a simple <acronym>SRF</> returning a composite type looks like:
<programlisting>
PG_FUNCTION_INFO_V1(testpassbyval);
+
Datum
testpassbyval(PG_FUNCTION_ARGS)
{
@@ -1801,7 +1900,7 @@ testpassbyval(PG_FUNCTION_ARGS)
int call_cntr;
int max_calls;
TupleDesc tupdesc;
- TupleTableSlot *slot;
+ TupleTableSlot *slot;
AttInMetadata *attinmeta;
/* stuff done only on the first call of the function */
@@ -1818,9 +1917,7 @@ testpassbyval(PG_FUNCTION_ARGS)
/* total number of tuples to be returned */
funcctx->max_calls = PG_GETARG_UINT32(0);
- /*
- * Build a tuple description for a __testpassbyval tuple
- */
+ /* Build a tuple description for a __testpassbyval tuple */
tupdesc = RelationNameGetTupleDesc("__testpassbyval");
/* allocate a slot for a tuple with this tupdesc */
@@ -1830,7 +1927,7 @@ testpassbyval(PG_FUNCTION_ARGS)
funcctx->slot = slot;
/*
- * Generate attribute metadata needed later to produce tuples from raw
+ * generate attribute metadata needed later to produce tuples from raw
* C strings
*/
attinmeta = TupleDescGetAttInMetadata(tupdesc);
@@ -1856,7 +1953,7 @@ testpassbyval(PG_FUNCTION_ARGS)
/*
* Prepare a values array for storage in our slot.
* This should be an array of C strings which will
- * be processed later by the appropriate "in" functions.
+ * be processed later by the type input functions.
*/
values = (char **) palloc(3 * sizeof(char *));
values[0] = (char *) palloc(16 * sizeof(char));
@@ -1873,150 +1970,36 @@ testpassbyval(PG_FUNCTION_ARGS)
/* make the tuple into a datum */
result = TupleGetDatum(slot, tuple);
- /* Clean up (this is not actually necessary) */
+ /* clean up (this is not really necessary) */
pfree(values[0]);
pfree(values[1]);
pfree(values[2]);
pfree(values);
- SRF_RETURN_NEXT(funcctx, result);
+ SRF_RETURN_NEXT(funcctx, result);
}
else /* do when there is no more left */
{
- SRF_RETURN_DONE(funcctx);
+ SRF_RETURN_DONE(funcctx);
}
}
</programlisting>
- with supporting SQL code of
+
+ The SQL code to declare this function is:
<programlisting>
-CREATE TYPE __testpassbyval AS (f1 int4, f2 int4, f3 int4);
+CREATE TYPE __testpassbyval AS (f1 integer, f2 integer, f3 integer);
-CREATE OR REPLACE FUNCTION testpassbyval(int4, int4) RETURNS setof __testpassbyval
- AS 'MODULE_PATHNAME','testpassbyval' LANGUAGE 'c' IMMUTABLE STRICT;
+CREATE OR REPLACE FUNCTION testpassbyval(integer, integer) RETURNS SETOF __testpassbyval
+ AS '<replaceable>filename</>', 'testpassbyval'
+ LANGUAGE C IMMUTABLE STRICT;
</programlisting>
</para>
<para>
- See <filename>contrib/tablefunc</> for more examples of table functions.
- </para>
-
- </sect3>
-
- </sect2>
-
- <sect2>
- <title>Writing Code</title>
-
- <para>
- We now turn to the more difficult task of writing
- programming language functions. Be warned: this section
- of the manual will not make you a programmer. You must
- have a good understanding of <acronym>C</acronym>
- (including the use of pointers)
- before trying to write <acronym>C</acronym> functions for
- use with <productname>PostgreSQL</productname>. While it may
- be possible to load functions written in languages other
- than <acronym>C</acronym> into <productname>PostgreSQL</productname>,
- this is often difficult (when it is possible at all)
- because other languages, such as <acronym>FORTRAN</acronym>
- and <acronym>Pascal</acronym> often do not follow the same
- <firstterm>calling convention</firstterm>
- as <acronym>C</acronym>. That is, other
- languages do not pass argument and return values
- between functions in the same way. For this reason, we
- will assume that your programming language functions
- are written in <acronym>C</acronym>.
- </para>
-
- <para>
- The basic rules for building <acronym>C</acronym> functions
- are as follows:
-
- <itemizedlist>
- <listitem>
- <para>
- Use <literal>pg_config --includedir-server</literal><indexterm><primary>pg_config</></> to find
- out where the <productname>PostgreSQL</> server header files are installed on
- your system (or the system that your users will be running
- on). This option is new with <productname>PostgreSQL</> 7.2.
- For <productname>PostgreSQL</>
- 7.1 you should use the option <option>--includedir</option>.
- (<command>pg_config</command> will exit with a non-zero status
- if it encounters an unknown option.) For releases prior to
- 7.1 you will have to guess, but since that was before the
- current calling conventions were introduced, it is unlikely
- that you want to support those releases.
- </para>
- </listitem>
-
- <listitem>
- <para>
- When allocating memory, use the
- <productname>PostgreSQL</productname> routines
- <function>palloc</function> and <function>pfree</function>
- instead of the corresponding <acronym>C</acronym> library
- routines <function>malloc</function> and
- <function>free</function>. The memory allocated by
- <function>palloc</function> will be freed automatically at the
- end of each transaction, preventing memory leaks.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Always zero the bytes of your structures using
- <function>memset</function> or <function>bzero</function>.
- Several routines (such as the hash access method, hash join
- and the sort algorithm) compute functions of the raw bits
- contained in your structure. Even if you initialize all
- fields of your structure, there may be several bytes of
- alignment padding (holes in the structure) that may contain
- garbage values.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Most of the internal <productname>PostgreSQL</productname> types
- are declared in <filename>postgres.h</filename>, while the function
- manager interfaces (<symbol>PG_FUNCTION_ARGS</symbol>, etc.)
- are in <filename>fmgr.h</filename>, so you will need to
- include at least these two files. For portability reasons it's best
- to include <filename>postgres.h</filename> <emphasis>first</>,
- before any other system or user header files.
- Including <filename>postgres.h</filename> will also include
- <filename>elog.h</filename> and <filename>palloc.h</filename>
- for you.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Symbol names defined within object files must not conflict
- with each other or with symbols defined in the
- <productname>PostgreSQL</productname> server executable. You
- will have to rename your functions or variables if you get
- error messages to this effect.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Compiling and linking your object code so that
- it can be dynamically loaded into
- <productname>PostgreSQL</productname>
- always requires special flags.
- See <xref linkend="dfunc">
- for a detailed explanation of how to do it for
- your particular operating system.
- </para>
- </listitem>
- </itemizedlist>
+ The directory <filename>contrib/tablefunc</> in the source
+ distribution contains more examples of set-returning functions.
</para>
</sect2>
-
-&dfunc;
-
</sect1>
<sect1 id="xfunc-overload">
@@ -2035,9 +2018,11 @@ CREATE OR REPLACE FUNCTION testpassbyval(int4, int4) RETURNS setof __testpassbyv
</para>
<para>
- A function may also have the same name as an attribute. In the case
- that there is an ambiguity between a function on a complex type and
- an attribute of the complex type, the attribute will always be used.
+ A function may also have the same name as an attribute. (Recall
+ that <literal>attribute(table)</literal> is equivalent to
+ <literal>table.attribute</literal>.) In the case that there is an
+ ambiguity between a function on a complex type and an attribute of
+ the complex type, the attribute will always be used.
</para>
<para>
@@ -2056,7 +2041,7 @@ CREATE FUNCTION test(smallint, double precision) RETURNS ...
</para>
<para>
- When overloading C language functions, there is an additional
+ When overloading C-language functions, there is an additional
constraint: The C name of each function in the family of
overloaded functions must be different from the C names of all
other functions, either internal or dynamically loaded. If this
@@ -2076,85 +2061,6 @@ CREATE FUNCTION test(int, int) RETURNS int
</programlisting>
The names of the C functions here reflect one of many possible conventions.
</para>
-
- <para>
- Prior to <productname>PostgreSQL</productname> 7.0, this
- alternative syntax did not exist. There is a trick to get around
- the problem, by defining a set of C functions with different names
- and then define a set of identically-named SQL function wrappers
- that take the appropriate argument types and call the matching C
- function.
- </para>
- </sect1>
-
- <sect1 id="xfunc-tablefunctions">
- <title>Table Functions</title>
-
- <indexterm zone="xfunc-tablefunctions"><primary>function</></>
-
- <para>
- Table functions are functions that produce a set of rows, made up of
- either base (scalar) data types, or composite (multi-column) data types.
- They are used like a table, view, or subselect in the <literal>FROM</>
- clause of a query. Columns returned by table functions may be included in
- <literal>SELECT</>, <literal>JOIN</>, or <literal>WHERE</> clauses in the
- same manner as a table, view, or subselect column.
- </para>
-
- <para>
- If a table function returns a base data type, the single result column
- is named for the function. If the function returns a composite type, the
- result columns get the same names as the individual attributes of the type.
- </para>
-
- <para>
- A table function may be aliased in the <literal>FROM</> clause, but it also
- may be left unaliased. If a function is used in the FROM clause with no
- alias, the function name is used as the relation name.
- </para>
-
- <para>
- Table functions work wherever tables do in <literal>SELECT</> statements.
- For example
-<programlisting>
-CREATE TABLE foo (fooid int, foosubid int, fooname text);
-
-CREATE FUNCTION getfoo(int) RETURNS setof foo AS '
- SELECT * FROM foo WHERE fooid = $1;
-' LANGUAGE SQL;
-
-SELECT * FROM getfoo(1) AS t1;
-
-SELECT * FROM foo
-WHERE foosubid in (select foosubid from getfoo(foo.fooid) z
- where z.fooid = foo.fooid);
-
-CREATE VIEW vw_getfoo AS SELECT * FROM getfoo(1);
-SELECT * FROM vw_getfoo;
-</programlisting>
- are all valid statements.
- </para>
-
- <para>
- In some cases it is useful to define table functions that can return
- different column sets depending on how they are invoked. To support this,
- the table function can be declared as returning the pseudo-type
- <type>record</>. When such a function is used in a query, the expected
- row structure must be specified in the query itself, so that the system
- can know how to parse and plan the query. Consider this example:
-<programlisting>
-SELECT *
-FROM dblink('dbname=template1', 'select proname, prosrc from pg_proc')
- AS t1(proname name, prosrc text)
-WHERE proname LIKE 'bytea%';
-</programlisting>
- The <literal>dblink</> function executes a remote query (see
- <literal>contrib/dblink</>). It is declared to return <type>record</>
- since it might be used for any kind of query. The actual column set
- must be specified in the calling query so that the parser knows, for
- example, what <literal>*</> should expand to.
- </para>
-
</sect1>
<sect1 id="xfunc-plhandler">
@@ -2179,22 +2085,14 @@ WHERE proname LIKE 'bytea%';
<para>
The call handler for a procedural language is a
- <quote>normal</quote> function, which must be written in a
- compiled language such as C and registered with
- <productname>PostgreSQL</productname> as taking no arguments and
- returning the <type>language_handler</type> type.
- This special pseudo-type identifies the handler as a call handler
- and prevents it from being called directly in queries.
+ <quote>normal</quote> function that must be written in a compiled
+ language such as C, using the version-1 interface, and registered
+ with <productname>PostgreSQL</productname> as taking no arguments
+ and returning the type <type>language_handler</type>. This
+ special pseudotype identifies the function as a call handler and
+ prevents it from being called directly in SQL commands.
</para>
- <note>
- <para>
- In <productname>PostgreSQL</productname> 7.1 and later, call
- handlers must adhere to the <quote>version 1</quote> function
- manager interface, not the old-style interface.
- </para>
- </note>
-
<para>
The call handler is called in the same way as any other function:
It receives a pointer to a
@@ -2203,7 +2101,7 @@ WHERE proname LIKE 'bytea%';
is expected to return a <type>Datum</type> result (and possibly
set the <structfield>isnull</structfield> field of the
<structname>FunctionCallInfoData</structname> structure, if it wishes
- to return an SQL NULL result). The difference between a call
+ to return an SQL null result). The difference between a call
handler and an ordinary callee function is that the
<structfield>flinfo->fn_oid</structfield> field of the
<structname>FunctionCallInfoData</structname> structure will contain
@@ -2215,12 +2113,12 @@ WHERE proname LIKE 'bytea%';
</para>
<para>
- It's up to the call handler to fetch the
- <classname>pg_proc</classname> entry and to analyze the argument
- and return types of the called procedure. The AS clause from the
- <command>CREATE FUNCTION</command> of the procedure will be found
- in the <literal>prosrc</literal> attribute of the
- <classname>pg_proc</classname> table entry. This may be the source
+ It's up to the call handler to fetch the entry of the function from the system table
+ <classname>pg_proc</classname> and to analyze the argument
+ and return types of the called function. The <literal>AS</> clause from the
+ <command>CREATE FUNCTION</command> of the function will be found
+ in the <literal>prosrc</literal> column of the
+ <classname>pg_proc</classname> row. This may be the source
text in the procedural language itself (like for PL/Tcl), a
path name to a file, or anything else that tells the call handler
what to do in detail.
@@ -2231,11 +2129,11 @@ WHERE proname LIKE 'bytea%';
A call handler can avoid repeated lookups of information about the
called function by using the
<structfield>flinfo->fn_extra</structfield> field. This will
- initially be NULL, but can be set by the call handler to point at
- information about the PL function. On subsequent calls, if
- <structfield>flinfo->fn_extra</structfield> is already non-NULL
+ initially be <symbol>NULL</>, but can be set by the call handler to point at
+ information about the called function. On subsequent calls, if
+ <structfield>flinfo->fn_extra</structfield> is already non-<symbol>NULL</>
then it can be used and the information lookup step skipped. The
- call handler must be careful that
+ call handler must make sure that
<structfield>flinfo->fn_extra</structfield> is made to point at
memory that will live at least until the end of the current query,
since an <structname>FmgrInfo</structname> data structure could be
@@ -2244,23 +2142,23 @@ WHERE proname LIKE 'bytea%';
<structfield>flinfo->fn_mcxt</structfield>; such data will
normally have the same lifespan as the
<structname>FmgrInfo</structname> itself. But the handler could
- also choose to use a longer-lived context so that it can cache
+ also choose to use a longer-lived memory context so that it can cache
function definition information across queries.
</para>
<para>
- When a PL function is invoked as a trigger, no explicit arguments
- are passed, but the
+ When a procedural-language function is invoked as a trigger, no arguments
+ are passed in the usual way, but the
<structname>FunctionCallInfoData</structname>'s
<structfield>context</structfield> field points at a
- <structname>TriggerData</structname> node, rather than being NULL
+ <structname>TriggerData</structname> structure, rather than being <symbol>NULL</>
as it is in a plain function call. A language handler should
- provide mechanisms for PL functions to get at the trigger
+ provide mechanisms for procedural-language functions to get at the trigger
information.
</para>
<para>
- This is a template for a PL handler written in C:
+ This is a template for a procedural-language handler written in C:
<programlisting>
#include "postgres.h"
#include "executor/spi.h"
@@ -2288,7 +2186,8 @@ plsample_call_handler(PG_FUNCTION_ARGS)
retval = ...
}
- else {
+ else
+ {
/*
* Called as a function
*/
@@ -2299,27 +2198,23 @@ plsample_call_handler(PG_FUNCTION_ARGS)
return retval;
}
</programlisting>
- </para>
-
- <para>
Only a few thousand lines of code have to be added instead of the
- dots to complete the call handler. See <xref linkend="xfunc-c">
- for information on how to compile it into a loadable module.
+ dots to complete the call handler.
</para>
<para>
- The following commands then register the sample procedural
- language:
+ After having compiled the handler function into a loadable module
+ (see <xref linkend="dfunc">), the following commands then
+ register the sample procedural language:
<programlisting>
-CREATE FUNCTION plsample_call_handler () RETURNS language_handler
- AS '/usr/local/pgsql/lib/plsample'
+CREATE FUNCTION plsample_call_handler() RETURNS language_handler
+ AS '<replaceable>filename</replaceable>'
LANGUAGE C;
CREATE LANGUAGE plsample
HANDLER plsample_call_handler;
</programlisting>
</para>
</sect1>
- </chapter>
<!-- Keep this comment at the end of the file
Local variables:
diff --git a/doc/src/sgml/xoper.sgml b/doc/src/sgml/xoper.sgml
index 24c74cd8b60c96e179c5f2cfb3bcee0f9a6e0f96..22d214623baefa829bcf73742203b732a2b953b1 100644
--- a/doc/src/sgml/xoper.sgml
+++ b/doc/src/sgml/xoper.sgml
@@ -1,25 +1,9 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.22 2003/01/15 19:35:35 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.23 2003/04/10 01:22:45 petere Exp $
-->
- <Chapter Id="xoper">
- <Title>Extending <Acronym>SQL</Acronym>: Operators</Title>
-
- <sect1 id="xoper-intro">
- <title>Introduction</title>
-
- <Para>
- <ProductName>PostgreSQL</ProductName> supports left unary,
- right unary, and binary
- operators. Operators can be overloaded; that is,
- the same operator name can be used for different operators
- that have different numbers and types of operands. If
- there is an ambiguous situation and the system cannot
- determine the correct operator to use, it will return
- an error. You may have to type-cast the left and/or
- right operands to help it understand which operator you
- meant to use.
- </Para>
+ <sect1 id="xoper">
+ <title>User-defined Operators</title>
<Para>
Every operator is <quote>syntactic sugar</quote> for a call to an
@@ -28,13 +12,18 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.22 2003/01/15 19:35:35 tgl E
the operator. However, an operator is <emphasis>not merely</emphasis>
syntactic sugar, because it carries additional information
that helps the query planner optimize queries that use the
- operator. Much of this chapter will be devoted to explaining
+ operator. The next section will be devoted to explaining
that additional information.
</Para>
- </sect1>
- <sect1 id="xoper-example">
- <title>Example</title>
+ <Para>
+ <productname>PostgreSQL</productname> supports left unary, right
+ unary, and binary operators. Operators can be overloaded; that is,
+ the same operator name can be used for different operators that
+ have different numbers and types of operands. When a query is
+ executed, the system determines the operator to call from the
+ number and types of the provided operands.
+ </Para>
<Para>
Here is an example of creating an operator for adding two complex
@@ -45,7 +34,7 @@ $Header: /cvsroot/pgsql/doc/src/sgml/xoper.sgml,v 1.22 2003/01/15 19:35:35 tgl E
<ProgramListing>
CREATE FUNCTION complex_add(complex, complex)
RETURNS complex
- AS '<replaceable>PGROOT</replaceable>/tutorial/complex'
+ AS '<replaceable>filename</replaceable>', 'complex_add'
LANGUAGE C;
CREATE OPERATOR + (
@@ -58,7 +47,7 @@ CREATE OPERATOR + (
</Para>
<Para>
- Now we can do:
+ Now we could execute a query like this:
<screen>
SELECT (a + b) AS c FROM test_complex;
@@ -78,20 +67,13 @@ SELECT (a + b) AS c FROM test_complex;
<command>CREATE OPERATOR</command>. The <literal>commutator</>
clause shown in the example is an optional hint to the query
optimizer. Further details about <literal>commutator</> and other
- optimizer hints appear below.
+ optimizer hints appear in the next section.
</Para>
</sect1>
<sect1 id="xoper-optimization">
<title>Operator Optimization Information</title>
- <note>
- <title>Author</title>
- <para>
- Written by Tom Lane.
- </para>
- </note>
-
<para>
A <ProductName>PostgreSQL</ProductName> operator definition can include
several optional clauses that tell the system useful things about how
@@ -99,7 +81,7 @@ SELECT (a + b) AS c FROM test_complex;
appropriate, because they can make for considerable speedups in execution
of queries that use the operator. But if you provide them, you must be
sure that they are right! Incorrect use of an optimization clause can
- result in backend crashes, subtly wrong output, or other Bad Things.
+ result in server process crashes, subtly wrong output, or other Bad Things.
You can always leave out an optimization clause if you are not sure
about it; the only consequence is that queries might run slower than
they need to.
@@ -112,7 +94,7 @@ SELECT (a + b) AS c FROM test_complex;
</para>
<sect2>
- <title>COMMUTATOR</title>
+ <title><literal>COMMUTATOR</></title>
<para>
The <literal>COMMUTATOR</> clause, if provided, names an operator that is the
@@ -155,7 +137,7 @@ SELECT (a + b) AS c FROM test_complex;
<para>
The other, more straightforward way is just to include <literal>COMMUTATOR</> clauses
in both definitions. When <ProductName>PostgreSQL</ProductName> processes
- the first definition and realizes that <literal>COMMUTATOR</> refers to a non-existent
+ the first definition and realizes that <literal>COMMUTATOR</> refers to a nonexistent
operator, the system will make a dummy entry for that operator in the
system catalog. This dummy entry will have valid data only
for the operator name, left and right operand types, and result type,
@@ -164,9 +146,7 @@ SELECT (a + b) AS c FROM test_complex;
dummy entry. Later, when you define the second operator, the system
updates the dummy entry with the additional information from the second
definition. If you try to use the dummy operator before it's been filled
- in, you'll just get an error message. (Note: This procedure did not work
- reliably in <ProductName>PostgreSQL</ProductName> versions before 6.5,
- but it is now the recommended way to do things.)
+ in, you'll just get an error message.
</para>
</listitem>
</itemizedlist>
@@ -174,7 +154,7 @@ SELECT (a + b) AS c FROM test_complex;
</sect2>
<sect2>
- <title>NEGATOR</title>
+ <title><literal>NEGATOR</></title>
<para>
The <literal>NEGATOR</> clause, if provided, names an operator that is the
@@ -194,14 +174,14 @@ SELECT (a + b) AS c FROM test_complex;
<para>
An operator's negator must have the same left and/or right operand types
- as the operator itself, so just as with <literal>COMMUTATOR</>, only the operator
+ as the operator to be defined, so just as with <literal>COMMUTATOR</>, only the operator
name need be given in the <literal>NEGATOR</> clause.
</para>
<para>
Providing a negator is very helpful to the query optimizer since
it allows expressions like <literal>NOT (x = y)</> to be simplified into
- x <> y. This comes up more often than you might think, because
+ <literal>x <> y</>. This comes up more often than you might think, because
<literal>NOT</> operations can be inserted as a consequence of other rearrangements.
</para>
@@ -213,12 +193,12 @@ SELECT (a + b) AS c FROM test_complex;
</sect2>
<sect2>
- <title>RESTRICT</title>
+ <title><literal>RESTRICT</></title>
<para>
The <literal>RESTRICT</> clause, if provided, names a restriction selectivity
- estimation function for the operator (note that this is a function
- name, not an operator name). <literal>RESTRICT</> clauses only make sense for
+ estimation function for the operator. (Note that this is a function
+ name, not an operator name.) <literal>RESTRICT</> clauses only make sense for
binary operators that return <type>boolean</>. The idea behind a restriction
selectivity estimator is to guess what fraction of the rows in a
table will satisfy a <literal>WHERE</literal>-clause condition of the form
@@ -269,15 +249,15 @@ column OP constant
You can use <function>scalarltsel</> and <function>scalargtsel</> for comparisons on data types that
have some sensible means of being converted into numeric scalars for
range comparisons. If possible, add the data type to those understood
- by the routine <function>convert_to_scalar()</function> in <filename>src/backend/utils/adt/selfuncs.c</filename>.
- (Eventually, this routine should be replaced by per-data-type functions
+ by the function <function>convert_to_scalar()</function> in <filename>src/backend/utils/adt/selfuncs.c</filename>.
+ (Eventually, this function should be replaced by per-data-type functions
identified through a column of the <classname>pg_type</> system catalog; but that hasn't happened
yet.) If you do not do this, things will still work, but the optimizer's
estimates won't be as good as they could be.
</para>
<para>
- There are additional selectivity functions designed for geometric
+ There are additional selectivity estimation functions designed for geometric
operators in <filename>src/backend/utils/adt/geo_selfuncs.c</filename>: <function>areasel</function>, <function>positionsel</function>,
and <function>contsel</function>. At this writing these are just stubs, but you may want
to use them (or even better, improve them) anyway.
@@ -285,12 +265,12 @@ column OP constant
</sect2>
<sect2>
- <title>JOIN</title>
+ <title><literal>JOIN</></title>
<para>
The <literal>JOIN</> clause, if provided, names a join selectivity
- estimation function for the operator (note that this is a function
- name, not an operator name). <literal>JOIN</> clauses only make sense for
+ estimation function for the operator. (Note that this is a function
+ name, not an operator name.) <literal>JOIN</> clauses only make sense for
binary operators that return <type>boolean</type>. The idea behind a join
selectivity estimator is to guess what fraction of the rows in a
pair of tables will satisfy a <literal>WHERE</>-clause condition of the form
@@ -319,13 +299,13 @@ table1.column1 OP table2.column2
</sect2>
<sect2>
- <title>HASHES</title>
+ <title><literal>HASHES</></title>
<para>
The <literal>HASHES</literal> clause, if present, tells the system that
it is permissible to use the hash join method for a join based on this
- operator. <literal>HASHES</> only makes sense for binary operators that
- return <literal>boolean</>, and in practice the operator had better be
+ operator. <literal>HASHES</> only makes sense for a binary operator that
+ returns <literal>boolean</>, and in practice the operator had better be
equality for some data type.
</para>
@@ -340,33 +320,35 @@ table1.column1 OP table2.column2
<para>
In fact, logical equality is not good enough either; the operator
- had better represent pure bitwise equality, because the hash function
- will be computed on the memory representation of the values regardless
- of what the bits mean. For example, equality of
- time intervals is not bitwise equality; the interval equality operator
- considers two time intervals equal if they have the same
- duration, whether or not their endpoints are identical. What this means
- is that a join using <literal>=</literal> between interval fields would yield different
- results if implemented as a hash join than if implemented another way,
- because a large fraction of the pairs that should match will hash to
- different values and will never be compared by the hash join. But
- if the optimizer chose to use a different kind of join, all the pairs
- that the equality operator says are equal will be found.
- We don't want that kind of inconsistency, so we don't mark interval
- equality as hashable.
+ had better represent pure bitwise equality, because the hash
+ function will be computed on the memory representation of the
+ values regardless of what the bits mean. For example, the
+ polygon operator <literal>~=</literal>, which checks whether two
+ polygons are the same, is not bitwise equality, because two
+ polygons can be considered the same even if their vertices are
+ specified in a different order. What this means is that a join
+ using <literal>~=</literal> between polygon fields would yield
+ different results if implemented as a hash join than if
+ implemented another way, because a large fraction of the pairs
+ that should match will hash to different values and will never be
+ compared by the hash join. But if the optimizer chooses to use a
+ different kind of join, all the pairs that the operator
+ <literal>~=</literal> says are the same will be found. We don't
+ want that kind of inconsistency, so we don't mark the polygon
+ operator <literal>~=</literal> as hashable.
</para>
<para>
There are also machine-dependent ways in which a hash join might fail
to do the right thing. For example, if your data type
is a structure in which there may be uninteresting pad bits, it's unsafe
- to mark the equality operator <literal>HASHES</>. (Unless, perhaps, you write
- your other operators to ensure that the unused bits are always zero.)
+ to mark the equality operator <literal>HASHES</>. (Unless you write
+ your other operators and functions to ensure that the unused bits are always zero, which is the recommended strategy.)
Another example is that the floating-point data types are unsafe for hash
- joins. On machines that meet the <acronym>IEEE</> floating-point standard, minus
- zero and plus zero are different values (different bit patterns) but
+ joins. On machines that meet the <acronym>IEEE</> floating-point standard, negative
+ zero and positive zero are different values (different bit patterns) but
they are defined to compare equal. So, if the equality operator on floating-point data types were marked
- <literal>HASHES</>, a minus zero and a plus zero would probably not be matched up
+ <literal>HASHES</>, a negative zero and a positive zero would probably not be matched up
by a hash join, but they would be matched up by any other join process.
</para>
@@ -403,9 +385,9 @@ table1.column1 OP table2.column2
<para>
The <literal>MERGES</literal> clause, if present, tells the system that
- it is permissible to use the merge join method for a join based on this
- operator. <literal>MERGES</> only makes sense for binary operators that
- return <literal>boolean</>, and in practice the operator must represent
+ it is permissible to use the merge-join method for a join based on this
+ operator. <literal>MERGES</> only makes sense for a binary operator that
+ returns <literal>boolean</>, and in practice the operator must represent
equality for some data type or pair of data types.
</para>
@@ -420,7 +402,7 @@ table1.column1 OP table2.column2
data types had better be the same (or at least bitwise equivalent),
it is possible to merge-join two
distinct data types so long as they are logically compatible. For
- example, the <type>int2</type>-versus-<type>int4</type> equality operator
+ example, the <type>smallint</type>-versus-<type>integer</type> equality operator
is merge-joinable.
We only need sorting operators that will bring both data types into a
logically compatible sequence.
@@ -429,11 +411,11 @@ table1.column1 OP table2.column2
<para>
Execution of a merge join requires that the system be able to identify
four operators related to the merge-join equality operator: less-than
- comparison for the left input data type, less-than comparison for the
- right input data type, less-than comparison between the two data types, and
+ comparison for the left operand data type, less-than comparison for the
+ right operand data type, less-than comparison between the two data types, and
greater-than comparison between the two data types. (These are actually
four distinct operators if the merge-joinable operator has two different
- input data types; but when the input types are the same the three
+ operand data types; but when the operand types are the same the three
less-than operators are all the same operator.)
It is possible to
specify these operators individually by name, as the <literal>SORT1</>,
@@ -447,8 +429,8 @@ table1.column1 OP table2.column2
</para>
<para>
- The input data types of the four comparison operators can be deduced
- from the input types of the merge-joinable operator, so just as with
+ The operand data types of the four comparison operators can be deduced
+ from the operand types of the merge-joinable operator, so just as with
<literal>COMMUTATOR</>, only the operator names need be given in these
clauses. Unless you are using peculiar choices of operator names,
it's sufficient to write <literal>MERGES</> and let the system fill in
@@ -469,7 +451,7 @@ table1.column1 OP table2.column2
<listitem>
<para>
A merge-joinable equality operator must have a merge-joinable
- commutator (itself if the two data types are the same, or a related
+ commutator (itself if the two operand data types are the same, or a related
equality operator if they are different).
</para>
</listitem>
@@ -523,11 +505,8 @@ table1.column1 OP table2.column2
<literal><</> and <literal>></> respectively.
</para>
</note>
-
</sect2>
-
</sect1>
- </Chapter>
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Local variables:
diff --git a/doc/src/sgml/xtypes.sgml b/doc/src/sgml/xtypes.sgml
index 8242aee8c498b23a8602b82fde106405e0dd815c..97688d92621e8200348f1b116a36f599dde0236c 100644
--- a/doc/src/sgml/xtypes.sgml
+++ b/doc/src/sgml/xtypes.sgml
@@ -1,5 +1,9 @@
- <chapter id="xtypes">
- <title>Extending <acronym>SQL</acronym>: Types</title>
+<!--
+$Header: /cvsroot/pgsql/doc/src/sgml/xtypes.sgml,v 1.17 2003/04/10 01:22:45 petere Exp $
+-->
+
+ <sect1 id="xtypes">
+ <title>User-Defined Types</title>
<indexterm zone="xtypes">
<primary>data types</primary>
@@ -7,22 +11,20 @@
</indexterm>
<comment>
- This chapter needs to be updated for the version-1 function manager
+ This section needs to be updated for the version-1 function manager
interface.
</comment>
<para>
- As previously mentioned, there are two kinds of types in
- <productname>PostgreSQL</productname>: base types (defined in a
- programming language) and composite types. This chapter describes
- how to define new base types.
+ As described above, there are two kinds of data types in
+ <productname>PostgreSQL</productname>: base types and composite
+ types. This section describes how to define new base types.
</para>
<para>
The examples in this section can be found in
<filename>complex.sql</filename> and <filename>complex.c</filename>
- in the tutorial directory. Composite examples are in
- <filename>funcs.sql</filename>.
+ in the tutorial directory.
</para>
<para>
@@ -36,15 +38,15 @@
These functions determine how the type appears in strings (for input
by the user and output to the user) and how the type is organized in
memory. The input function takes a null-terminated character string
- as its input and returns the internal (in memory) representation of
+ as its argument and returns the internal (in memory) representation of
the type. The output function takes the internal representation of
- the type and returns a null-terminated character string.
+ the type as argument and returns a null-terminated character string.
</para>
<para>
- Suppose we want to define a complex type which represents complex
- numbers. Naturally, we would choose to represent a complex in memory
- as the following <acronym>C</acronym> structure:
+ Suppose we want to define a type <type>complex</> that represents
+ complex numbers. A natural way to to represent a complex number in
+ memory would be the following C structure:
<programlisting>
typedef struct Complex {
@@ -53,24 +55,16 @@ typedef struct Complex {
} Complex;
</programlisting>
- and a string of the form <literal>(x,y)</literal> as the external string
- representation.
+ As the external string representation of the type, we choose a
+ string of the form <literal>(x,y)</literal>.
</para>
<para>
- The functions are usually not hard to write, especially the output
- function. However, there are a number of points to remember:
-
- <itemizedlist>
- <listitem>
- <para>
- When defining your external (string) representation, remember
- that you must eventually write a complete and robust parser for
- that representation as your input function!
- </para>
-
- <para>
- For instance:
+ The input and output functions are usually not hard to write,
+ especially the output function. But when defining the external
+ string representation of the type, remember that you must eventually
+ write a complete and robust parser for that representation as your
+ input function. For instance:
<programlisting>
Complex *
@@ -78,48 +72,42 @@ complex_in(char *str)
{
double x, y;
Complex *result;
- if (sscanf(str, " ( %lf , %lf )", &x, &y) != 2) {
+
+ if (sscanf(str, " ( %lf , %lf )", &x, &y) != 2)
+ {
elog(ERROR, "complex_in: error in parsing %s", str);
return NULL;
}
- result = (Complex *)palloc(sizeof(Complex));
+ result = (Complex *) palloc(sizeof(Complex));
result->x = x;
result->y = y;
- return (result);
+ return result;
}
</programlisting>
- </para>
- <para>
- The output function can simply be:
+ The output function can simply be:
<programlisting>
char *
complex_out(Complex *complex)
{
char *result;
+
if (complex == NULL)
return(NULL);
result = (char *) palloc(60);
sprintf(result, "(%g,%g)", complex->x, complex->y);
- return(result);
+ return result;
}
</programlisting>
+ </para>
- </para>
- </listitem>
-
- <listitem>
- <para>
- You should try to make the input and output functions inverses of
- each other. If you do not, you will have severe problems when
- you need to dump your data into a file and then read it back in
- (say, into someone else's database on another computer). This is
- a particularly common problem when floating-point numbers are
- involved.
- </para>
- </listitem>
- </itemizedlist>
+ <para>
+ You should try to make the input and output functions inverses of
+ each other. If you do not, you will have severe problems when you
+ need to dump your data into a file and then read it back in. This
+ is a particularly common problem when floating-point numbers are
+ involved.
</para>
<para>
@@ -130,14 +118,18 @@ complex_out(Complex *complex)
<programlisting>
CREATE FUNCTION complex_in(cstring)
RETURNS complex
- AS '<replaceable>PGROOT</replaceable>/tutorial/complex'
+ AS '<replaceable>filename</replaceable>'
LANGUAGE C;
CREATE FUNCTION complex_out(complex)
RETURNS cstring
- AS '<replaceable>PGROOT</replaceable>/tutorial/complex'
+ AS '<replaceable>filename</replaceable>'
LANGUAGE C;
</programlisting>
+
+ Notice that the declarations of the input and output functions must
+ reference the not-yet-defined type. This is allowed, but will draw
+ warning messages that may be ignored.
</para>
<para>
@@ -149,49 +141,36 @@ CREATE TYPE complex (
output = complex_out
);
</programlisting>
-
- Notice that the declarations of the input and output functions must
- reference the not-yet-defined type. This is allowed, but will draw
- warning messages that may be ignored.
</para>
<para>
- <indexterm>
- <primary>arrays</primary>
- </indexterm>
- As discussed earlier, <productname>PostgreSQL</productname> fully
- supports arrays of base types. Additionally,
- <productname>PostgreSQL</productname> supports arrays of
- user-defined types as well. When you define a type,
+ When you define a new base type,
<productname>PostgreSQL</productname> automatically provides support
- for arrays of that type. For historical reasons, the array type has
- the same name as the user-defined type with the underscore character
- <literal>_</> prepended.
+ for arrays of that
+ type.<indexterm><primary>array</primary><secondary>of user-defined
+ type</secondary></indexterm> For historical reasons, the array type
+ has the same name as the base type with the underscore character
+ (<literal>_</>) prepended.
</para>
<para>
- Composite types do not need any function defined on them, since the
- system already understands what they look like inside.
+ If the values of your data type might exceed a few hundred bytes in
+ size (in internal form), you should mark them
+ TOAST-able.<indexterm><primary>TOAST</primary><secondary>and
+ user-defined types</secondary></indexterm> To do this, the internal
+ representation must follow the standard layout for variable-length
+ data: the first four bytes must be an <type>int32</type> containing
+ the total length in bytes of the datum (including itself). Also,
+ when running the <command>CREATE TYPE</command> command, specify the
+ internal length as <literal>variable</> and select the appropriate
+ storage option.
</para>
<para>
- <indexterm>
- <primary>TOAST</primary>
- <secondary>and user-defined types</secondary>
- </indexterm>
- If the values of your data type might exceed a few hundred bytes in
- size (in internal form), you should be careful to mark them
- TOAST-able. To do this, the internal representation must follow the
- standard layout for variable-length data: the first four bytes must
- be an <type>int32</type> containing the total length in bytes of the
- datum (including itself). Then, all your functions that accept
- values of the type must be careful to call
- <function>pg_detoast_datum()</function> on the supplied values ---
- after checking that the value is not NULL, if your function is not
- strict. Finally, select the appropriate storage option when giving
- the <command>CREATE TYPE</command> command.
+ For further details see the description of the <command>CREATE
+ TYPE</command> command in <xref linkend="reference">.
</para>
-</chapter>
+</sect1>
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