postgresql/doc/src/sgml/ref/create_function.sgml

<REFENTRY ID="SQL-CREATEFUNCTION">
 <REFMETA>
  <REFENTRYTITLE>
   CREATE FUNCTION
  </REFENTRYTITLE>
  <REFMISCINFO>SQL - Language Statements</REFMISCINFO>
 </REFMETA>
 <REFNAMEDIV>
  <REFNAME>
   CREATE FUNCTION
  </REFNAME>
  <REFPURPOSE>
   Defines a new function
  </REFPURPOSE>
 </refnamediv>
 <REFSYNOPSISDIV>
  <REFSYNOPSISDIVINFO>
   <DATE>1998-09-09</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">definition</replaceable>
    LANGUAGE '<replaceable class="parameter">langname</replaceable>'
  </SYNOPSIS>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-1">
   <REFSECT2INFO>
    <DATE>1998-09-09</DATE>
   </REFSECT2INFO>
   <TITLE>
    Inputs
   </TITLE>
   <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">definition</replaceable>
      </TERM>
      <LISTITEM>
       <PARA>
	A string defining the function; the meaning depends on the language.
	It may be an internal function name, the path to an object file,
	an SQL query, or text in a procedural language.
       </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 name of a created procedural
	language. See <command>CREATE LANGUAGE</command> for details.
       </PARA>
      </LISTITEM>
     </VARLISTENTRY>
    </variablelist>
   </para>
  </REFSECT2>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-2">
   <REFSECT2INFO>
    <DATE>1998-09-09</DATE>
   </REFSECT2INFO>
   <TITLE>
    Outputs
   </TITLE>
   <PARA>
    
    <VARIABLELIST>
     <VARLISTENTRY>
      <TERM>
       <ReturnValue>CREATE</ReturnValue>
      </TERM>
      <LISTITEM>
       <PARA>
	This is returned if the command completes successfully.
       </para>
      </listitem>
     </varlistentry>
    </VARIABLELIST>
   </para>
  </REFSECT2>
 </REFSYNOPSISDIV>
 
 <REFSECT1 ID="R1-SQL-CREATEFUNCTION-1">
  <REFSECT1INFO>
   <DATE>1998-09-09</DATE>
  </REFSECT1INFO>
  <TITLE>
   Description
  </TITLE>
  <PARA>
   <command>CREATE FUNCTION</command> allows a
   <productname>Postgres</productname> user
   to register a function
   with a database. Subsequently, this user is treated as the
   owner of the function.
  </PARA>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-3">
   <REFSECT2INFO>
    <DATE>1998-09-09</DATE>
   </REFSECT2INFO>
   <TITLE>
    Notes
   </TITLE>
   <PARA>
    Refer to the chapter on functions 
in the <citetitle>PostgreSQL Programmer's Guide</citetitle>
    for further information.
   </PARA>
   <PARA>
    Use <command>DROP FUNCTION</command>
    to drop user-defined functions.
   </PARA>

  <PARA>
   <productname>Postgres</productname> allows function "overloading";
   that is, the same name can be used for several different functions
   so long as they have distinct argument types.  This facility must be
   used with caution for INTERNAL and C-language functions, however.
  </PARA>

  <PARA>
   Two INTERNAL functions cannot have the same C name without causing
   errors at link time.  To get around that, give them different C names
   (for example, use the argument types as part of the C names), then
   specify those names in the AS clause of <command>CREATE FUNCTION</command>.
   If the AS clause is left empty then <command>CREATE FUNCTION</command>
   assumes the C name of the function is the same as the SQL name.
  </PARA>

  <PARA>
   For dynamically-loaded C functions, the SQL name of the function must
   be the same as the C function name, because the AS clause is used to
   give the path name of the object file containing the C code.  In this
   situation it is best not to try to overload SQL function names.  It
   might work to load a C function that has the same C name as an internal
   function or another dynamically-loaded function --- or it might not.
   On some platforms the dynamic loader may botch the load in interesting
   ways if there is a conflict of C function names.  So, even if it works
   for you today, you might regret overloading names later when you try
   to run the code somewhere else.
  </PARA>
  </REFSECT2>
 </refsect1>
  
 <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>
    <command>CREATE FUNCTION</command> is
 a <productname>Postgres</productname> language extension.
   </PARA>
  
  <REFSECT2 ID="R2-SQL-CREATEFUNCTION-4">
   <REFSECT2INFO>
    <DATE>1998-09-09</DATE>
   </REFSECT2INFO>
   <TITLE>
    SQL/PSM
   </TITLE>
   <para>

<note>
     <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. As of mid-1998, this
has not yet happened, but it is hoped that PSM will
      eventually become a standard.
     </para>
</note>

SQL/PSM <command>CREATE FUNCTION</command> has the following syntax:
<synopsis>
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>
</synopsis>

   </para>
  </refsect2>
 </refsect1>
</REFENTRY>

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