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375 lines
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375 lines
10 KiB
Plaintext
<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_language.sgml,v 1.9 2000/03/26 18:32:27 petere Exp $
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Postgres documentation
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-->
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<refentry id="SQL-CREATELANGUAGE">
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<refmeta>
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<refentrytitle id="sql-createlanguage-title">
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CREATE LANGUAGE
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</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>
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CREATE LANGUAGE
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</refname>
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<refpurpose>
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Defines a new language for functions
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</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>1999-07-20</date>
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</refsynopsisdivinfo>
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<synopsis>
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CREATE [ TRUSTED ] PROCEDURAL LANGUAGE '<replaceable class="parameter">langname</replaceable>'
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HANDLER <replaceable class="parameter">call_handler</replaceable>
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LANCOMPILER '<replaceable class="parameter">comment</replaceable>'
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</synopsis>
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<refsect2 id="R2-SQL-CREATELANGUAGE-1">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term>TRUSTED</term>
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<listitem>
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<para>
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<function> TRUSTED</function> specifies that the call handler for
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the language is safe; that is, it offers an unprivileged user
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no functionality to bypass access restrictions. If
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this keyword is omitted when registering the language,
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only users with the <productname>Postgres</productname>
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superuser privilege can use
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this language to create new functions
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(like the 'C' 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">langname</replaceable></term>
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<listitem>
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<para>
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The name of the new procedural language.
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The language name is case insensitive. A procedural
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language cannot override one of the built-in languages of
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<productname>Postgres</productname>.
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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>HANDLER <replaceable class="parameter">call_handler</replaceable></term>
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<listitem>
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<para>
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<replaceable class="parameter">call_handler</replaceable> is the name
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of a previously
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registered function that will be called to execute the PL
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procedures.
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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">comment</replaceable></term>
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<listitem>
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<para>
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The <function>LANCOMPILER</function> argument is the
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string that will be
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inserted in the <literal>LANCOMPILER</literal> attribute
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of the new
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<filename>pg_language</filename> entry. At present,
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<productname>Postgres</productname> does not use
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this attribute in any way.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-CREATELANGUAGE-2">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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CREATE
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</computeroutput></term>
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<listitem>
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<para>
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This message is returned if the language is successfully
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created.
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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><computeroutput>
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ERROR: PL handler function <replaceable class="parameter">funcname</replaceable>() doesn't exist
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</computeroutput></term>
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<listitem>
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<para>
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This error is returned if the function
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<replaceable class="parameter">funcname</replaceable>()
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is not found.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1 id="R1-SQL-CREATELANGUAGE-1">
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<refsect1info>
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<date>1998-09-09</date>
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</refsect1info>
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<title>
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Description
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</title>
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<para>
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Using <command>CREATE LANGUAGE</command>, a
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<productname>Postgres</productname> user can register
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a new language with <productname>Postgres</productname>.
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Subsequently, functions and
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trigger procedures can be defined in this new language.
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The user must have the <productname>Postgres</productname>
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superuser privilege to
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register a new language.
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</para>
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<refsect2 id="R2-SQL-CREATELANGUAGE-3">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Writing PL handlers
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</title>
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<para>
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The call handler for a procedural language must be written
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in a compiler language such as 'C' and registered with
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<productname>Postgres</productname> as a function taking
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no arguments and returning the
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<type>opaque</type> type, a placeholder for unspecified or undefined types..
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This prevents the call handler from being
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called directly as a function from queries.
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</para>
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<para>
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However, arguments must be supplied on the actual call when a
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PL function or trigger
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procedure in the language offered by the handler is to be
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executed.
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<itemizedlist>
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<listitem>
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<para>
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When called from the trigger manager, the only argument is
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the object ID from the procedure's <filename>pg_proc</filename>
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entry. All other
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information from the trigger manager is found in the
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global <structname>CurrentTriggerData</structname> pointer.
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</para>
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</listitem>
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<listitem>
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<para>
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When called from the function manager, the arguments are
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the object ID of the procedure's <filename>pg_proc</filename>
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entry, the number
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of arguments given to the PL function, the arguments in a
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<structname>FmgrValues</structname> structure and a pointer
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to a boolean where the
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function tells the caller if the return value is the SQL
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NULL value.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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It's up to the call handler to fetch the
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<filename>pg_proc</filename> entry and
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to analyze the argument and return types of the called
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procedure. The AS clause from the
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<command>CREATE FUNCTION</command> of
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the procedure will be found in the <literal>prosrc</literal>
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attribute of the
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<filename>pg_proc</filename> table entry. This may be the
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source text in the procedural
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language itself (like for PL/Tcl), a pathname to a
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file or anything else that tells the call handler what to
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do in detail.
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-CREATELANGUAGE-4">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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Notes
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</title>
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<para>
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Use <command>CREATE FUNCTION</command>
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to create a function.
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</para>
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<para>
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Use <command>DROP LANGUAGE</command> to drop procedural languages.
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</para>
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<para>
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Refer to the table <filename>pg_language</filename>
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for further information:
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<programlisting>
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<computeroutput>
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Table "pg_language"
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Attribute | Type | Modifier
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---------------+---------+----------
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lanname | name |
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lanispl | boolean |
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lanpltrusted | boolean |
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lanplcallfoid | oid |
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lancompiler | text |
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lanname | lanispl | lanpltrusted | lanplcallfoid | lancompiler
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----------+---------+--------------+---------------+-------------
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internal | f | f | 0 | n/a
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C | f | f | 0 | /bin/cc
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sql | f | f | 0 | postgres
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</computeroutput>
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</programlisting>
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</para>
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<para>
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Since the call handler for a procedural language must be
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registered with <productname>Postgres</productname> in the 'C' language,
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it inherits
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all the capabilities and restrictions of 'C' functions.
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</para>
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<para>
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At present, the definitions for a procedural language cannot be
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changed once they have been created.
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</para>
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</refsect2>
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</refsect1>
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<refsect1 id="R1-SQL-CREATELANGUAGE-6">
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<title>
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Usage
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</title>
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<para>
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This is a template for a PL handler written in 'C':
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<programlisting>
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#include "executor/spi.h"
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#include "commands/trigger.h"
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#include "utils/elog.h"
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#include "fmgr.h" /* for FmgrValues struct */
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#include "access/heapam.h"
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#include "utils/syscache.h"
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#include "catalog/pg_proc.h"
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#include "catalog/pg_type.h"
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Datum
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plsample_call_handler(
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Oid prooid,
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int pronargs,
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FmgrValues *proargs,
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bool *isNull)
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{
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Datum retval;
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TriggerData *trigdata;
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if (CurrentTriggerData == NULL) {
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/*
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* Called as a function
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*/
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retval = ...
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} else {
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/*
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* Called as a trigger procedure
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*/
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trigdata = CurrentTriggerData;
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CurrentTriggerData = NULL;
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retval = ...
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}
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*isNull = false;
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return retval;
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}
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</programlisting>
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</para>
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<para>
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Only a few thousand lines of code have to be added instead
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of the dots to complete the PL call handler.
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See <command>CREATE FUNCTION</command> for information on how to compile
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it into a loadable module.
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</para>
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<para>
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The following commands then register the sample procedural
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language:
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<programlisting>
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CREATE FUNCTION plsample_call_handler () RETURNS opaque
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AS '/usr/local/pgsql/lib/plsample.so'
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LANGUAGE 'C';
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CREATE PROCEDURAL LANGUAGE 'plsample'
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HANDLER plsample_call_handler
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LANCOMPILER 'PL/Sample';
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-CREATELANGUAGE-7">
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<title>
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Compatibility
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</title>
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<refsect2 id="R2-SQL-CREATELANGUAGE-5">
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<refsect2info>
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<date>1998-09-09</date>
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</refsect2info>
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<title>
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SQL92
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</title>
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<para>
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<command>CREATE LANGUAGE</command>
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is a <productname>Postgres</productname> extension.
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There is no <command>CREATE LANGUAGE</command> statement in
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<acronym>SQL92</acronym>.
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</para>
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</refsect2>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:nil
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../reference.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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sgml-local-ecat-files:nil
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End:
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-->
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