mirror of
https://github.com/postgres/postgres.git
synced 2025-05-31 00:01:57 -04:00
294 lines
8.1 KiB
Plaintext
294 lines
8.1 KiB
Plaintext
<!--
|
|
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_trigger.sgml,v 1.17 2001/09/13 18:17:44 petere Exp $
|
|
Postgres documentation
|
|
-->
|
|
|
|
<refentry id="SQL-CREATETRIGGER">
|
|
<docinfo>
|
|
<date>2001-09-13</date>
|
|
</docinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle id="SQL-CREATETRIGGER-TITLE">CREATE TRIGGER</refentrytitle>
|
|
<refmiscinfo>SQL - Language Statements</refmiscinfo>
|
|
</refmeta>
|
|
<refnamediv>
|
|
<refname>
|
|
CREATE TRIGGER
|
|
</refname>
|
|
<refpurpose>
|
|
define a new trigger
|
|
</refpurpose>
|
|
</refnamediv>
|
|
<refsynopsisdiv>
|
|
<refsynopsisdivinfo>
|
|
<date>2000-03-25</date>
|
|
</refsynopsisdivinfo>
|
|
<synopsis>
|
|
CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTER } { <replaceable class="PARAMETER">event</replaceable> [OR ...] }
|
|
ON <replaceable class="PARAMETER">table</replaceable> FOR EACH { ROW | STATEMENT }
|
|
EXECUTE PROCEDURE <replaceable class="PARAMETER">func</replaceable> ( <replaceable class="PARAMETER">arguments</replaceable> )
|
|
</synopsis>
|
|
|
|
<refsect2 id="R2-SQL-CREATETRIGGER-1">
|
|
<refsect2info>
|
|
<date>1998-09-21</date>
|
|
</refsect2info>
|
|
<title>
|
|
Inputs
|
|
</title>
|
|
<para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><replaceable class="parameter">name</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
The name of an existing trigger.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><replaceable class="parameter">table</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
The name of a table.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><replaceable class="parameter">event</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
One of INSERT, DELETE or UPDATE.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><replaceable class="parameter">func</replaceable></term>
|
|
<listitem>
|
|
<para>
|
|
A user-supplied function.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</refsect2>
|
|
|
|
<refsect2 id="R2-SQL-CREATETRIGGER-2">
|
|
<refsect2info>
|
|
<date>1998-09-21</date>
|
|
</refsect2info>
|
|
<title>
|
|
Outputs
|
|
</title>
|
|
<para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><computeroutput>
|
|
CREATE
|
|
</computeroutput></term>
|
|
<listitem>
|
|
<para>
|
|
This message is returned if the trigger is successfully created.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
</refsect2>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1 id="R1-SQL-CREATETRIGGER-1">
|
|
<refsect1info>
|
|
<date>1998-09-21</date>
|
|
</refsect1info>
|
|
<title>
|
|
Description
|
|
</title>
|
|
|
|
<para>
|
|
<command>CREATE TRIGGER</command> will enter a new trigger into the current
|
|
data base. The trigger will be associated with the relation
|
|
<replaceable class="parameter">table</replaceable> and will execute
|
|
the specified function <replaceable class="parameter">func</replaceable>.
|
|
</para>
|
|
|
|
<para>
|
|
The trigger can be specified to fire either before BEFORE the
|
|
operation is attempted on a tuple (before constraints
|
|
are checked and the <command>INSERT</command>, <command>UPDATE</command> or
|
|
<command>DELETE</command> is attempted) or
|
|
AFTER the operation has been attempted (e.g., after constraints
|
|
are checked and the <command>INSERT</command>,
|
|
<command>UPDATE</command> or <command>DELETE</command> has
|
|
completed). If the
|
|
trigger fires before the event, the trigger may
|
|
skip the operation for the current tuple, or change the tuple
|
|
being inserted (for <command>INSERT</command> and
|
|
<command>UPDATE</command> operations only). If
|
|
the trigger fires after the event, all changes, including the
|
|
last insertion, update, or deletion, are <quote>visible</quote> to the trigger.
|
|
</para>
|
|
|
|
<para>
|
|
Refer to the chapters on SPI and Triggers in the
|
|
<citetitle>PostgreSQL Programmer's Guide</citetitle> for more
|
|
information.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1 id="SQL-CREATETRIGGER-notes">
|
|
<title>Notes</title>
|
|
|
|
<para>
|
|
To create a trigger on a table, the user must have the
|
|
<literal>TRIGGER</literal> privilege on the table.
|
|
</para>
|
|
|
|
<para>
|
|
As of the current release, <literal>STATEMENT</literal> triggers are not implemented.
|
|
</para>
|
|
|
|
<para>
|
|
Refer to the <xref linkend="sql-droptrigger"> command for
|
|
information on how to remove triggers.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1 id="R1-SQL-CREATETRIGGER-2">
|
|
<title>Examples</title>
|
|
|
|
<para>
|
|
Check if the specified distributor code exists in the distributors
|
|
table before appending or updating a row in the table films:
|
|
|
|
<programlisting>
|
|
CREATE TRIGGER if_dist_exists
|
|
BEFORE INSERT OR UPDATE ON films FOR EACH ROW
|
|
EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
Before cancelling a distributor or updating its code, remove every
|
|
reference to the table films:
|
|
<programlisting>
|
|
CREATE TRIGGER if_film_exists
|
|
BEFORE DELETE OR UPDATE ON distributors FOR EACH ROW
|
|
EXECUTE PROCEDURE check_foreign_key (1, 'CASCADE', 'did', 'films', 'did');
|
|
</programlisting>
|
|
</para>
|
|
|
|
<para>
|
|
The second example can also be done by using a foreign key,
|
|
constraint as in:
|
|
|
|
<programlisting>
|
|
CREATE TABLE distributors (
|
|
did DECIMAL(3),
|
|
name VARCHAR(40),
|
|
CONSTRAINT if_film_exists
|
|
FOREIGN KEY(did) REFERENCES films
|
|
ON UPDATE CASCADE ON DELETE CASCADE
|
|
);
|
|
</programlisting>
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1 id="SQL-CREATETRIGGER-compatibility">
|
|
<title>Compatibility</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>SQL92</term>
|
|
<listitem>
|
|
<para>
|
|
There is no <command>CREATE TRIGGER</command> statement in <acronym>SQL92</acronym>.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>SQL99</term>
|
|
<listitem>
|
|
<para>
|
|
The <command>CREATE TRIGGER</command> statement in
|
|
<productname>PostgreSQL</productname> implements a subset of the
|
|
SQL99 standard. The following functionality is missing:
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
SQL99 allows triggers to fire on updates to specific columns
|
|
(e.g., <literal>AFTER UPDATE OF col1, col2</literal>).
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
SQL99 allows you to define aliases for the <quote>old</quote>
|
|
and <quote>new</quote> rows or tables for use in the definiton
|
|
of the triggered action (e.g., <literal>CREATE TRIGGER ... ON
|
|
tablename REFERENCING OLD ROW AS somename NEW ROW AS
|
|
othername ...</literal>). Since
|
|
<productname>PostgreSQL</productname> allows trigger
|
|
procedures to be written in any number of user-defined
|
|
languages, access to the data is handled in a
|
|
language-specific way.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<productname>PostgreSQL</productname> only has row-level
|
|
triggers, no statement-level triggers.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
<productname>PostgreSQL</productname> only allows the
|
|
execution of a stored procedure for the triggered action.
|
|
SQL99 allows the execution of a number of other SQL commands,
|
|
such as <command>CREATE TABLE</command> as triggered action.
|
|
This limitation is not hard to work around by creating a
|
|
stored procedure that executes these commands.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
|
|
<simplelist type="inline">
|
|
<member><xref linkend="sql-createfunction"></member>
|
|
<member><xref linkend="sql-droptrigger"></member>
|
|
<member><citetitle>PostgreSQL Programmer's Guide</citetitle></member>
|
|
</simplelist>
|
|
</refsect1>
|
|
</refentry>
|
|
|
|
<!-- Keep this comment at the end of the file
|
|
Local variables:
|
|
mode: sgml
|
|
sgml-omittag:nil
|
|
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
|
|
sgml-local-catalogs:"/usr/lib/sgml/catalog"
|
|
sgml-local-ecat-files:nil
|
|
End:
|
|
-->
|