From 77fe28f33e49d752be4e4a1bbc6c112f825e7882 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 3 May 2001 17:50:55 +0000
Subject: [PATCH] Describe handling of multiply-inherited fields correctly.
---
doc/src/sgml/ref/create_table.sgml | 64 +++++++++++++++++++++---------
1 file changed, 46 insertions(+), 18 deletions(-)
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index 8a7796c5751..fb5e2b2a550 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -1,5 +1,5 @@
<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.41 2001/02/04 12:18:08 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_table.sgml,v 1.42 2001/05/03 17:50:55 tgl Exp $
Postgres documentation
-->
@@ -26,7 +26,7 @@ Postgres documentation
CREATE [ TEMPORARY | TEMP ] TABLE <replaceable class="PARAMETER">table_name</replaceable> (
{ <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">type</replaceable> [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
| <replaceable>table_constraint</replaceable> } [, ... ]
- ) [ INHERITS ( <replaceable>inherited_table</replaceable> [, ... ] ) ]
+ ) [ INHERITS ( <replaceable>parent_table</replaceable> [, ... ] ) ]
where <replaceable class="PARAMETER">column_constraint</replaceable> can be:
[ CONSTRAINT <replaceable class="PARAMETER">constraint_name</replaceable> ]
@@ -99,17 +99,11 @@ and <replaceable class="PARAMETER">table_constraint</replaceable> can be:
</varlistentry>
<varlistentry>
- <term><replaceable class="PARAMETER">inherited_table</replaceable></term>
+ <term><replaceable class="PARAMETER">parent_table</replaceable></term>
<listitem>
<para>
The optional INHERITS clause specifies a list of table
names from which this table automatically inherits all fields.
- If any inherited field name appears more than once,
- <productname>Postgres</productname>
- reports an error.
- <productname>Postgres</productname> automatically allows the created
- table to inherit functions on tables above it in the inheritance
- hierarchy.
</para>
</listitem>
</varlistentry>
@@ -258,20 +252,54 @@ ERROR: Relation '<replaceable class="parameter">table</replaceable>' already ex
existing datatype.
</para>
+ <para>
+ A table can have no more than 1600 columns (in practice, the
+ effective limit is lower because of tuple-length constraints).
+ A table cannot have the same name as a system catalog table.
+ </para>
+ </refsect1>
+
+ <refsect1 id="R1-SQL-INHERITSCLAUSE-1">
+ <title id="R1-SQL-INHERITSCLAUSE-1-TITLE">
+ INHERITS Clause
+ </title>
+ <para>
+ <synopsis>
+INHERITS ( <replaceable class="PARAMETER">parent_table</replaceable> [, ... ] )
+ </synopsis>
+ </para>
+
<para>
The optional INHERITS
- clause specifies a collection of table names from which this table
- automatically inherits all fields. If any inherited field name
- appears more than once, Postgres reports an error. Postgres automatically
- allows the created table to inherit functions on tables above it in
- the inheritance hierarchy. Inheritance of functions is done according
- to the conventions of the Common Lisp Object System (CLOS).
+ clause specifies a list of table names from which the new table
+ automatically inherits all fields. If the same field name appears in
+ more than one parent table, Postgres reports an error unless the field
+ definitions match in each of the parent tables. If there is no
+ definition conflict, then the duplicate fields are merged to form a single
+ field of the new table. If the new table's own field list contains a
+ field name that is also inherited, this declaration must likewise match
+ the inherited field(s), and the field definitions are merged into one.
</para>
<para>
- A table can have no more than 1600 columns (in practice, the
- effective limit is lower because of tuple-length constraints).
- A table cannot have the same name as a system catalog table.
+ Inherited and new field declarations of the same name must specify exactly
+ the same data type to avoid an error. They need not specify identical
+ constraints --- all constraints provided from any declaration are merged
+ together and all are applied to the new table. If the new table explicitly
+ specifies a default value for the field, this default overrides any
+ defaults from inherited declarations of the field. Otherwise, any parents
+ that specify default values for the field must all specify the same
+ default, or an error will be reported.
+ </para>
+
+ <para>
+ Postgres automatically allows the created table to inherit functions on
+ tables above it in the inheritance hierarchy; that is, if we create table
+ <literal>foo</literal> inheriting from <literal>bar</literal>, then
+ functions that accept the tuple type <literal>bar</literal> can also be
+ applied to instances of <literal>foo</literal>. (Currently, this works
+ reliably for functions on the first or only parent table, but not so well
+ for functions on additional parents.)
</para>
</refsect1>
--
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