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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_function.sgml,v 1.41 2002/07/24 19:11:07 petere Exp $
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-->
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1999-06-14 09:37:05 +02:00
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<refentry id="SQL-CREATEFUNCTION">
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<refmeta>
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2001-11-18 21:35:02 +01:00
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<refentrytitle id="SQL-CREATEFUNCTION-TITLE">CREATE FUNCTION</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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1999-06-14 09:37:05 +02:00
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<refnamediv>
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2001-05-19 11:01:10 +02:00
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<refname>CREATE FUNCTION</refname>
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<refpurpose>define a new function</refpurpose>
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</refnamediv>
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1999-06-14 09:37:05 +02:00
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<refsynopsisdiv>
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<synopsis>
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CREATE [ OR REPLACE ] FUNCTION <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argtype</replaceable> [, ...] ] )
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RETURNS <replaceable class="parameter">rettype</replaceable>
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{ LANGUAGE <replaceable class="parameter">langname</replaceable>
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| IMMUTABLE | STABLE | VOLATILE
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| CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT
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| [EXTERNAL] SECURITY INVOKER | [EXTERNAL] SECURITY DEFINER
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| AS '<replaceable class="parameter">definition</replaceable>'
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| AS '<replaceable class="parameter">obj_file</replaceable>', '<replaceable class="parameter">link_symbol</replaceable>'
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} ...
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[ WITH ( <replaceable class="parameter">attribute</replaceable> [, ...] ) ]
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</synopsis>
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</refsynopsisdiv>
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1998-05-13 07:34:00 +02:00
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2001-05-19 11:01:10 +02:00
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<refsect1 id="sql-createfunction-description">
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<title>Description</title>
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1999-07-06 19:16:42 +02:00
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<para>
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<command>CREATE FUNCTION</command> defines a new function.
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<command>CREATE OR REPLACE FUNCTION</command> will either create a
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new function, or replace an existing definition.
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</para>
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<para>
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The user that creates the function becomes the owner of the function.
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</para>
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1999-07-06 19:16:42 +02:00
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2001-05-19 11:01:10 +02:00
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<variablelist>
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<title>Parameters</title>
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<varlistentry>
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<term><replaceable class="parameter">name</replaceable></term>
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<listitem>
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<para>
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The name of a function to create. If a schema name is included,
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then the function is created in the
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specified schema. Otherwise it is created in the current schema (the
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one at the front of the search path; see <literal>CURRENT_SCHEMA()</>).
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The name of the new function must not match any existing function
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with the same argument types in the same schema. However, functions of
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different argument types may share a name (this is called
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<firstterm>overloading</>).
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">argtype</replaceable></term>
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<listitem>
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<para>
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The data type(s) of the function's arguments, if any. The
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2001-06-05 01:27:23 +02:00
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input types may be base or complex types,
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<literal>opaque</literal>, or the same as the type of an
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existing column. <literal>Opaque</literal> indicates
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that the function accepts arguments of a non-SQL type such as
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<type>char *</type>.
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The type of a column is indicated using <replaceable
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class="parameter">tablename</replaceable>.<replaceable
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class="parameter">columnname</replaceable><literal>%TYPE</literal>;
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using this can sometimes help make a function independent from
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changes to the definition of a table.
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2001-05-19 11:01:10 +02:00
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">rettype</replaceable></term>
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<listitem>
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<para>
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The return data type. The return type may be specified as a
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2001-06-05 01:27:23 +02:00
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base type, complex type, <literal>setof</literal> type,
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<literal>opaque</literal>, or the same as the type of an
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existing column.
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The <literal>setof</literal>
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modifier indicates that the function will return a set of
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items, rather than a single item. Functions with a declared
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return type of <literal>opaque</literal> do not return a value.
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These cannot be called directly; trigger functions make use of
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this feature.
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</para>
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</listitem>
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</varlistentry>
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2002-05-17 20:32:52 +02:00
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<varlistentry>
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<term><replaceable class="parameter">langname</replaceable></term>
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<listitem>
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<para>
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The name of the language that the function is implemented in.
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May be <literal>SQL</literal>, <literal>C</literal>,
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<literal>internal</literal>, or the name of a user-defined
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procedural language. (See also <xref linkend="app-createlang"
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endterm="app-createlang-title">.) For backward compatibility,
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the name may be enclosed by single quotes.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>IMMUTABLE</term>
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<term>STABLE</term>
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<term>VOLATILE</term>
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<listitem>
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<para>
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These attributes inform the system whether it is safe to
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replace multiple evaluations of the function with a single
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evaluation, for run-time optimization. At most one choice
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should be specified. If none of these appear,
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<literal>VOLATILE</literal> is the default assumption.
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</para>
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<para>
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<literal>IMMUTABLE</literal> indicates that the function always
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returns the same result when given the same argument values; that
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is, it does not do database lookups or otherwise use information not
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directly present in its parameter list. If this option is given,
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any call of the function with all-constant arguments can be
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immediately replaced with the function value.
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</para>
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<para>
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<literal>STABLE</literal> indicates that within a single table scan
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the function will consistently
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return the same result for the same argument values, but that its
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result could change across SQL statements. This is the appropriate
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selection for functions whose results depend on database lookups,
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parameter variables (such as the current time zone), etc. Also note
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that the <literal>CURRENT_TIMESTAMP</> family of functions qualify
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as stable, since their values do not change within a transaction.
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</para>
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<para>
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<literal>VOLATILE</literal> indicates that the function value can
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change even within a single table scan, so no optimizations can be
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made. Relatively few database functions are volatile in this sense;
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some examples are <literal>random()</>, <literal>currval()</>,
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<literal>timeofday()</>. Note that any function that has side-effects
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must be classified volatile, even if its result is quite predictable,
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to prevent calls from being optimized away; an example is
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<literal>setval()</>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>CALLED ON NULL INPUT</term>
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<term>RETURNS NULL ON NULL INPUT</term>
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<term>STRICT</term>
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<listitem>
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<para>
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<literal>CALLED ON NULL INPUT</literal> (the default) indicates
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that the function will be called normally when some of its
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arguments are null. It is then the function author's
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responsibility to check for NULLs if necessary and respond
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appropriately.
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</para>
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<para>
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<literal>RETURNS NULL ON NULL INPUT</literal> or
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<literal>STRICT</literal> indicates that the function always
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returns NULL whenever any of its arguments are NULL. If this
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parameter is specified, the function is not executed when there
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are NULL arguments; instead a NULL result is assumed
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automatically.
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</para>
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</listitem>
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</varlistentry>
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2002-05-18 15:48:01 +02:00
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<varlistentry>
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<term><optional>EXTERNAL</optional> SECURITY INVOKER</term>
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<term><optional>EXTERNAL</optional> SECURITY DEFINER</term>
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<listitem>
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<para>
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<literal>SECURITY INVOKER</literal> indicates that the function
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is to be executed with the privileges of the user that calls it.
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That is the default. <literal>SECURITY DEFINER</literal>
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specifies that the function is to be executed with the
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privileges of the user that created it.
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</para>
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<para>
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The key word <literal>EXTERNAL</literal> is present for SQL
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compatibility but is optional since, unlike in SQL, this feature
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does not only apply to external functions.
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</para>
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</listitem>
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</varlistentry>
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2001-05-19 11:01:10 +02:00
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<varlistentry>
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<term><replaceable class="parameter">definition</replaceable></term>
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<listitem>
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<para>
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A string defining the function; the meaning depends on the
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language. It may be an internal function name, the path to an
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object file, an SQL query, or text in a procedural language.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">obj_file</replaceable>, <replaceable class="parameter">link_symbol</replaceable></term>
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<listitem>
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<para>
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This form of the <literal>AS</literal> clause is used for
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dynamically linked C language functions when the function name
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in the C language source code is not the same as the name of
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the SQL function. The string <replaceable
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class="parameter">obj_file</replaceable> is the name of the
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file containing the dynamically loadable object, and
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<replaceable class="parameter">link_symbol</replaceable> is the
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object's link symbol, that is, the name of the function in the C
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language source code.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">attribute</replaceable></term>
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<listitem>
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<para>
|
2002-05-17 20:32:52 +02:00
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The historical way to specify optional pieces of information
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about the function. The following attributes may appear here:
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<variablelist>
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<varlistentry>
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<term>isStrict</term>
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<listitem>
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|
<para>
|
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Equivalent to <literal>STRICT</literal> or <literal>RETURNS NULL ON NULL INPUT</literal>
|
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</para>
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|
</listitem>
|
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</varlistentry>
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<varlistentry>
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<term>isCachable</term>
|
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|
<listitem>
|
|
|
|
<para>
|
|
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|
<literal>isCachable</literal> is an obsolete equivalent of
|
2002-07-24 21:11:14 +02:00
|
|
|
<literal>IMMUTABLE</literal>; it's still accepted for
|
2002-05-17 20:32:52 +02:00
|
|
|
backwards-compatibility reasons.
|
|
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|
</para>
|
|
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|
</listitem>
|
|
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|
</varlistentry>
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</variablelist>
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Attribute names are not case-sensitive.
|
|
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|
</para>
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|
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|
</listitem>
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|
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|
</varlistentry>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
</variablelist>
|
2000-08-25 01:36:29 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
</refsect1>
|
2000-08-25 01:36:29 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<refsect1 id="sql-createfunction-notes">
|
|
|
|
<title>Notes</title>
|
2000-03-27 19:14:43 +02:00
|
|
|
|
1999-06-14 09:37:05 +02:00
|
|
|
<para>
|
2000-03-27 19:14:43 +02:00
|
|
|
Refer to the chapter in the
|
|
|
|
<citetitle>PostgreSQL Programmer's Guide</citetitle>
|
|
|
|
on the topic of extending
|
2001-12-08 04:24:40 +01:00
|
|
|
<productname>PostgreSQL</productname> via functions
|
1999-07-22 17:09:15 +02:00
|
|
|
for further information on writing external functions.
|
1999-06-14 09:37:05 +02:00
|
|
|
</para>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
2000-03-27 19:14:43 +02:00
|
|
|
<para>
|
2001-05-19 11:01:10 +02:00
|
|
|
The full <acronym>SQL</acronym> type syntax is allowed for
|
2000-03-27 19:14:43 +02:00
|
|
|
input arguments and return value. However, some details of the
|
2000-10-05 21:48:34 +02:00
|
|
|
type specification (e.g., the precision field for
|
2000-03-27 19:14:43 +02:00
|
|
|
<type>numeric</type> types) are the responsibility of the
|
|
|
|
underlying function implementation and are silently swallowed
|
2000-08-25 01:36:29 +02:00
|
|
|
(i.e., not recognized or
|
2000-03-27 19:14:43 +02:00
|
|
|
enforced) by the <command>CREATE FUNCTION</command> command.
|
|
|
|
</para>
|
1999-05-20 04:57:15 +02:00
|
|
|
|
1999-07-22 17:09:15 +02:00
|
|
|
<para>
|
2001-12-08 04:24:40 +01:00
|
|
|
<productname>PostgreSQL</productname> allows function <firstterm>overloading</firstterm>;
|
2000-08-25 01:36:29 +02:00
|
|
|
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>
|
2000-11-20 21:36:57 +01:00
|
|
|
Two <literal>internal</literal>
|
1999-07-22 17:09:15 +02:00
|
|
|
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>.
|
2000-10-05 21:48:34 +02:00
|
|
|
If the AS clause is left empty, then <command>CREATE FUNCTION</command>
|
1999-07-22 17:09:15 +02:00
|
|
|
assumes the C name of the function is the same as the SQL name.
|
|
|
|
</para>
|
1999-05-20 04:57:15 +02:00
|
|
|
|
1999-07-22 17:09:15 +02:00
|
|
|
<para>
|
2000-08-25 01:36:29 +02:00
|
|
|
Similarly, when overloading SQL function names with multiple C-language
|
|
|
|
functions, give
|
|
|
|
each C-language instance of the function a distinct name, then use
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
the alternative form of the <command>AS</command> clause in the
|
2000-08-25 01:36:29 +02:00
|
|
|
<command>CREATE FUNCTION</command> syntax to select the appropriate
|
|
|
|
C-language implementation of each overloaded SQL function.
|
1999-07-22 17:09:15 +02:00
|
|
|
</para>
|
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<para>
|
|
|
|
When repeated <command>CREATE FUNCTION</command> calls refer to
|
|
|
|
the same object file, the file is only loaded once. To unload and
|
|
|
|
reload the file (perhaps during development), use the <xref
|
2001-11-18 21:35:02 +01:00
|
|
|
linkend="sql-load" endterm="sql-load-title"> command.
|
2001-05-19 11:01:10 +02:00
|
|
|
</para>
|
|
|
|
|
2001-10-02 23:39:36 +02:00
|
|
|
<para>
|
|
|
|
Use <command>DROP FUNCTION</command>
|
|
|
|
to remove user-defined functions.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
To update the definition of an existing function, use
|
|
|
|
<command>CREATE OR REPLACE FUNCTION</command>. Note that it is
|
|
|
|
not possible to change the name or argument types of a function
|
|
|
|
this way (if you tried, you'd just be creating a new, distinct
|
|
|
|
function). Also, <command>CREATE OR REPLACE FUNCTION</command>
|
|
|
|
will not let you change the return type of an existing function.
|
|
|
|
To do that, you must drop and re-create the function.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
If you drop and then re-create a function, the new function is not
|
|
|
|
the same entity as the old; you will break existing rules, views,
|
|
|
|
triggers, etc that referred to the old function. Use
|
|
|
|
<command>CREATE OR REPLACE FUNCTION</command> to change a function
|
|
|
|
definition without breaking objects that refer to the function.
|
|
|
|
</para>
|
|
|
|
|
2002-02-19 00:11:58 +01:00
|
|
|
<para>
|
|
|
|
To be able to define a function, the user must have the
|
|
|
|
<literal>USAGE</literal> privilege on the language.
|
|
|
|
</para>
|
|
|
|
|
|
|
|
<para>
|
|
|
|
By default, only the owner (creator) of the function has the right
|
|
|
|
to execute it. Other users must be granted the
|
|
|
|
<literal>EXECUTE</literal> privilege on the function to be able to
|
|
|
|
use it.
|
|
|
|
</para>
|
1998-12-29 03:24:47 +01:00
|
|
|
</refsect1>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
<refsect1 id="sql-createfunction-examples">
|
|
|
|
<title>Examples</title>
|
|
|
|
|
1999-06-14 09:37:05 +02:00
|
|
|
<para>
|
1998-05-13 07:34:00 +02:00
|
|
|
To create a simple SQL function:
|
1999-07-06 19:16:42 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<programlisting>
|
|
|
|
CREATE FUNCTION one() RETURNS integer
|
|
|
|
AS 'SELECT 1 AS RESULT;'
|
2001-08-13 23:34:54 +02:00
|
|
|
LANGUAGE SQL;
|
1999-07-06 19:16:42 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
SELECT one() AS answer;
|
|
|
|
<computeroutput>
|
2000-03-26 20:32:30 +02:00
|
|
|
answer
|
|
|
|
--------
|
|
|
|
1
|
2001-05-19 11:01:10 +02:00
|
|
|
</computeroutput>
|
|
|
|
</programlisting>
|
1999-07-06 19:16:42 +02:00
|
|
|
</para>
|
|
|
|
|
1998-05-13 07:34:00 +02:00
|
|
|
<para>
|
2001-05-19 11:01:10 +02:00
|
|
|
The next example creates a C function by calling a routine from a
|
2001-10-26 23:17:03 +02:00
|
|
|
user-created shared library named <filename>funcs.so</> (the extension
|
|
|
|
may vary across platforms). The shared library file is sought in the
|
|
|
|
server's dynamic library search path. This particular routine calculates
|
2002-05-17 20:32:52 +02:00
|
|
|
a check digit and returns true if the check digit in the function
|
2001-05-19 11:01:10 +02:00
|
|
|
parameters is correct. It is intended for use in a CHECK
|
|
|
|
constraint.
|
|
|
|
|
|
|
|
<programlisting>
|
|
|
|
CREATE FUNCTION ean_checkdigit(char, char) RETURNS boolean
|
2001-10-26 23:17:03 +02:00
|
|
|
AS 'funcs' LANGUAGE C;
|
1998-12-29 03:24:47 +01:00
|
|
|
|
1999-07-06 19:16:42 +02:00
|
|
|
CREATE TABLE product (
|
1999-06-14 09:37:05 +02:00
|
|
|
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))
|
1999-07-06 19:16:42 +02:00
|
|
|
);
|
2001-05-19 11:01:10 +02:00
|
|
|
</programlisting>
|
|
|
|
</para>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
|
|
|
|
<para>
|
2002-05-17 20:32:52 +02:00
|
|
|
The next example creates a function that does type conversion from the
|
2002-04-11 22:00:18 +02:00
|
|
|
user-defined type complex to the built-in type point. The
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
function is implemented by a dynamically loaded object that was
|
2001-10-26 23:17:03 +02:00
|
|
|
compiled from C source (we illustrate the now-deprecated alternative
|
2002-03-22 20:20:45 +01:00
|
|
|
of specifying the absolute file name to the shared object file).
|
2001-10-26 23:17:03 +02:00
|
|
|
For <productname>PostgreSQL</productname> to
|
2001-05-19 11:01:10 +02:00
|
|
|
find a type conversion function automatically, the SQL function has
|
2000-08-25 01:36:29 +02:00
|
|
|
to have the same name as the return type, and so overloading is
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
unavoidable. The function name is overloaded by using the second
|
2000-07-22 04:39:10 +02:00
|
|
|
form of the <command>AS</command> clause in the SQL definition:
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
<programlisting>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
CREATE FUNCTION point(complex) RETURNS point
|
|
|
|
AS '/home/bernie/pgsql/lib/complex.so', 'complex_to_point'
|
2002-05-17 20:32:52 +02:00
|
|
|
LANGUAGE C STRICT;
|
2001-05-19 11:01:10 +02:00
|
|
|
</programlisting>
|
|
|
|
|
|
|
|
The C declaration of the function could be:
|
|
|
|
|
|
|
|
<programlisting>
|
I have been working with user defined types and user defined c
functions. One problem that I have encountered with the function
manager is that it does not allow the user to define type conversion
functions that convert between user types. For instance if mytype1,
mytype2, and mytype3 are three Postgresql user types, and if I wish to
define Postgresql conversion functions like
I run into problems, because the Postgresql dynamic loader would look
for a single link symbol, mytype3, for both pieces of object code. If
I just change the name of one of the Postgresql functions (to make the
symbols distinct), the automatic type conversion that Postgresql uses,
for example, when matching operators to arguments no longer finds the
type conversion function.
The solution that I propose, and have implemented in the attatched
patch extends the CREATE FUNCTION syntax as follows. In the first case
above I use the link symbol mytype2_to_mytype3 for the link object
that implements the first conversion function, and define the
Postgresql operator with the following syntax
The patch includes changes to the parser to include the altered
syntax, changes to the ProcedureStmt node in nodes/parsenodes.h,
changes to commands/define.c to handle the extra information in the AS
clause, and changes to utils/fmgr/dfmgr.c that alter the way that the
dynamic loader figures out what link symbol to use. I store the
string for the link symbol in the prosrc text attribute of the pg_proc
table which is currently unused in rows that reference dynamically
loaded
functions.
Bernie Frankpitt
1999-09-28 06:34:56 +02:00
|
|
|
Point * complex_to_point (Complex *z)
|
|
|
|
{
|
|
|
|
Point *p;
|
|
|
|
|
|
|
|
p = (Point *) palloc(sizeof(Point));
|
|
|
|
p->x = z->x;
|
|
|
|
p->y = z->y;
|
|
|
|
|
|
|
|
return p;
|
|
|
|
}
|
2001-05-19 11:01:10 +02:00
|
|
|
</programlisting>
|
2002-04-05 02:31:36 +02:00
|
|
|
|
|
|
|
Note that the function is marked <quote>strict</>; this allows us
|
|
|
|
to skip checking for NULL input in the function body.
|
2001-05-19 11:01:10 +02:00
|
|
|
</para>
|
1999-06-14 09:37:05 +02:00
|
|
|
</refsect1>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
1998-05-13 07:34:00 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<refsect1 id="sql-createfunction-compat">
|
|
|
|
<title>Compatibility</title>
|
1999-07-22 17:09:15 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
<para>
|
|
|
|
A <command>CREATE FUNCTION</command> command is defined in SQL99.
|
|
|
|
The <application>PostgreSQL</application> version is similar but
|
2002-05-17 20:32:52 +02:00
|
|
|
not fully compatible. The attributes are not portable, neither are the
|
2001-05-19 11:01:10 +02:00
|
|
|
different available languages.
|
|
|
|
</para>
|
|
|
|
</refsect1>
|
1998-09-16 16:43:12 +02:00
|
|
|
|
2001-05-19 11:01:10 +02:00
|
|
|
|
|
|
|
<refsect1 id="sql-createfunction-seealso">
|
|
|
|
<title>See Also</title>
|
|
|
|
|
|
|
|
<para>
|
2002-05-17 20:32:52 +02:00
|
|
|
<xref linkend="sql-dropfunction" endterm="sql-dropfunction-title">,
|
|
|
|
<xref linkend="sql-grant" endterm="sql-grant-title">,
|
|
|
|
<xref linkend="sql-load" endterm="sql-load-title">,
|
|
|
|
<xref linkend="sql-revoke" endterm="sql-revoke-title">,
|
|
|
|
<xref linkend="app-createlang">,
|
2001-05-19 11:01:10 +02:00
|
|
|
<citetitle>PostgreSQL Programmer's Guide</citetitle>
|
|
|
|
</para>
|
1998-05-13 07:34:00 +02:00
|
|
|
</refsect1>
|
2001-05-19 11:01:10 +02:00
|
|
|
|
1999-06-14 09:37:05 +02:00
|
|
|
</refentry>
|
1998-05-13 07:34:00 +02:00
|
|
|
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
|
|
Local variables:
|
2000-03-27 19:14:43 +02:00
|
|
|
mode:sgml
|
1999-06-14 09:37:05 +02:00
|
|
|
sgml-omittag:nil
|
1998-05-13 07:34:00 +02:00
|
|
|
sgml-shorttag:t
|
|
|
|
sgml-minimize-attributes:nil
|
|
|
|
sgml-always-quote-attributes:t
|
|
|
|
sgml-indent-step:1
|
|
|
|
sgml-indent-data:t
|
|
|
|
sgml-parent-document:nil
|
|
|
|
sgml-default-dtd-file:"../reference.ced"
|
|
|
|
sgml-exposed-tags:nil
|
2000-03-27 19:14:43 +02:00
|
|
|
sgml-local-catalogs:("/usr/lib/sgml/catalog")
|
1998-05-13 07:34:00 +02:00
|
|
|
sgml-local-ecat-files:nil
|
|
|
|
End:
|
|
|
|
-->
|