create_function.sgml

<REFENTRY ID="SQL-CREATEFUNCTION-1">
 <REFMETA>
  <REFENTRYTITLE>
   CREATE FUNCTION
  </REFENTRYTITLE>
  <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
 </REFMETA>
 <REFNAMEDIV>
  <REFNAME>
   CREATE FUNCTION
  </REFNAME>
  <REFPURPOSE>
   Defines a new function
  </REFPURPOSE>
  
 <REFSYNOPSISDIV>
  <REFSYNOPSISDIVINFO>
   <DATE>1998-04-15</DATE>
  </REFSYNOPSISDIVINFO>
  <SYNOPSIS>
   CREATE FUNCTION <replaceable class="parameter">name</replaceable> ([<replaceable class="parameter">ftype</replaceable> [, ...]])
             RETURNS <replaceable class="parameter">rtype</replaceable>
             AS <replaceable class="parameter">path</replaceable>
             LANGUAGE '<replaceable class="parameter">langname</replaceable>'
  </SYNOPSIS>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-1">
   <REFSECT2INFO>
    <DATE>1998-04-15</DATE>
   </REFSECT2INFO>
   <TITLE>
    Inputs
   </TITLE>
   <PARA>
   </PARA>
   <VARIABLELIST>
    <VARLISTENTRY>
     <TERM>
     </TERM>
     <LISTITEM>
      <PARA>
       <VARIABLELIST>
	<VARLISTENTRY>
	 <TERM>
	  <replaceable class="parameter">name</replaceable>
	 </TERM>
	 <LISTITEM>
	  <PARA>
           The name of a function to create.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
	<VARLISTENTRY>
	 <TERM>
	  <replaceable class="parameter">ftype</replaceable>
	 </TERM>
	 <LISTITEM>
	  <PARA>
           The data type of function arguments.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
	<VARLISTENTRY>
	 <TERM>
	  <replaceable class="parameter">rtype</replaceable>
	 </TERM>
	 <LISTITEM>
	  <PARA>
           The return data type.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
	<VARLISTENTRY>
	 <TERM>
	  <replaceable class="parameter">path</replaceable>
	 </TERM>
	 <LISTITEM>
	  <PARA>
	   May be either an SQL-query or an absolute path to an
           object file.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
	<VARLISTENTRY>
	 <TERM>
	  <replaceable class="parameter">langname</replaceable>
	 </TERM>
	 <LISTITEM>
	  <PARA>
           may be '<literal>c</literal>', '<literal>sql</literal>', '<literal>internal</literal>' or '<replaceable class="parameter">plname</replaceable>'.
           (where '<replaceable class="parameter">plname</replaceable>' is the language name of a created procedural
           language. See <command>CREATE LANGUAGE</command> for details).
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
       </variablelist>
     </LISTITEM>
    </VARLISTENTRY>
   </VARIABLELIST>
  </REFSECT2>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-2">
   <REFSECT2INFO>
    <DATE>1998-04-15</DATE>
   </REFSECT2INFO>
   <TITLE>
    Outputs
   </TITLE>
   <PARA>
   </PARA>
   <VARIABLELIST>
    <VARLISTENTRY>
     <TERM>
     </TERM>
     <LISTITEM>
      <PARA>
       <VARIABLELIST>
	<VARLISTENTRY>
	 <TERM>
	  <ReturnValue>CREATE</ReturnValue>
	 </TERM>
	 <LISTITEM>
	  <PARA>
	   This is returned if the command completes successfully.
	  </PARA>
	 </LISTITEM>
	</VARLISTENTRY>
       </variablelist>
     </LISTITEM>
    </VARLISTENTRY>
   </VARIABLELIST>
  </REFSECT2>
 </REFSYNOPSISDIV>
 
 <REFSECT1 ID="R1-SQL-CREATEFUNCTION-1">
  <REFSECT1INFO>
   <DATE>1998-04-15</DATE>
  </REFSECT1INFO>
  <TITLE>
   Description
  </TITLE>
  <PARA>
   With this command, a PostgreSQL user can register a function
   with PostgreSQL. Subsequently, this user is treated as the
   owner of the function.
  </PARA>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-3">
   <REFSECT2INFO>
    <DATE>1998-04-15</DATE>
   </REFSECT2INFO>
   <TITLE>
    Notes
   </TITLE>
   <PARA>
    Refer to <citetitle>PostgreSQL User's Guide</citetitle> chapter 6 for further information.
    <comment>This reference needs to be corrected.</comment>
   </PARA>
   <PARA>
    Refer to the <citerefentry>
     <refentrytitle>DROP FUNCTION</refentrytitle>
    </citerefentry> statement to drop functions.
   </PARA>
  </REFSECT2>
  
 <REFSECT1 ID="R1-SQL-CREATEFUNCTION-2">
  <TITLE>
   Usage
  </TITLE>
  <PARA>
   To create a simple SQL function:
  </PARA>
  <ProgramListing>
   CREATE FUNCTION one() RETURNS int4
            AS 'SELECT 1 AS RESULT'
                LANGUAGE 'sql';

   SELECT one() AS answer;

   <computeroutput>answer 
   ------
   1   </computeroutput>
  </ProgramListing>
  <para>
   To create a C function, calling a routine from a user-created
   shared library.  This particular routine calculates a check
   digit and returns TRUE if the check digit in the function parameters
   is correct. It is intended for use in a CHECK contraint.
  </para>
  <programlisting>
   <userinput>CREATE FUNCTION ean_checkdigit(bpchar, bpchar) RETURNS bool
                AS '/usr1/proj/bray/sql/funcs.so' LANGUAGE 'c';

   CREATE TABLE product
   (
        id              char(8)         PRIMARY KEY,
        eanprefix       char(8)         CHECK (eanprefix ~ '[0-9]{2}-[0-9]{5}')
                                        REFERENCES brandname(ean_prefix),
        eancode         char(6)         CHECK (eancode ~ '[0-9]{6}'),
        CONSTRAINT ean CHECK (ean_checkdigit(eanprefix, eancode))
   );</userinput>
  </programlisting>
 </REFSECT1>
 
 <REFSECT1 ID="R1-SQL-CREATEFUNCTION-3">
  <TITLE>
   Bugs
  </TITLE>
  <PARA>
   A C function cannot return a set of values.
  </PARA>
 </REFSECT1>
 
 <REFSECT1 ID="R1-SQL-CREATEFUNCTION-4">
  <TITLE>
   Compatibility
  </TITLE>
   <PARA>
    The CREATE FUNCTION statement is a PostgreSQL language extension.
   </PARA>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-4">
   <REFSECT2INFO>
    <DATE>1998-04-15</DATE>
   </REFSECT2INFO>
   <TITLE>
    SQL/PSM<footnote>
     <para>
      PSM stands for Persistent Stored Modules, it is a procedural
      language and it was originally hoped that PSM would be ratified
      as an official standard by late 1996. However PSM will
      eventually become a standard.
     </para>
    </footnote>
   </TITLE>
   <para>
    The SQL/PSM CREATE FUNCTION statement has the following syntax:
   <programlisting>
     CREATE FUNCTION <replaceable class="parameter">name</replaceable>
            ( [ [IN|OUT|INOUT] <replaceable class="parameter">parm</replaceable> <replaceable class="parameter">type</replaceable> [, ...] ])
            RETURNS <replaceable class="parameter">rtype</replaceable>
            LANGUAGE '<replaceable class="parameter">langname</replaceable>'
            ESPECIFIC <replaceable class="parameter">routine</replaceable>
            <replaceable class="parameter">SQL-statement</replaceable>
   </programlisting>
   </para>
  </refsect2>
 </refsect1>
</REFENTRY>


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