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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:19:15 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-04 12:19:15 +0000
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+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>9.28. Trigger Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="functions-admin.html" title="9.27. System Administration Functions" /><link rel="next" href="functions-event-triggers.html" title="9.29. Event Trigger Functions" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">9.28. Trigger Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="functions-admin.html" title="9.27. System Administration Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><th width="60%" align="center">Chapter 9. Functions and Operators</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="functions-event-triggers.html" title="9.29. Event Trigger Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="FUNCTIONS-TRIGGER"><div class="titlepage"><div><div><h2 class="title" style="clear: both">9.28. Trigger Functions</h2></div></div></div><p>
+ While many uses of triggers involve user-written trigger functions,
+ <span class="productname">PostgreSQL</span> provides a few built-in trigger
+ functions that can be used directly in user-defined triggers. These
+ are summarized in <a class="xref" href="functions-trigger.html#BUILTIN-TRIGGERS-TABLE" title="Table 9.97. Built-In Trigger Functions">Table 9.97</a>.
+ (Additional built-in trigger functions exist, which implement foreign
+ key constraints and deferred index constraints. Those are not documented
+ here since users need not use them directly.)
+ </p><p>
+ For more information about creating triggers, see
+ <a class="xref" href="sql-createtrigger.html" title="CREATE TRIGGER"><span class="refentrytitle">CREATE TRIGGER</span></a>.
+ </p><div class="table" id="BUILTIN-TRIGGERS-TABLE"><p class="title"><strong>Table 9.97. Built-In Trigger Functions</strong></p><div class="table-contents"><table class="table" summary="Built-In Trigger Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
+ Function
+ </p>
+ <p>
+ Description
+ </p>
+ <p>
+ Example Usage
+ </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
+ <a id="id-1.5.8.34.4.2.2.1.1.1.1" class="indexterm"></a>
+ <code class="function">suppress_redundant_updates_trigger</code> ( )
+ → <code class="returnvalue">trigger</code>
+ </p>
+ <p>
+ Suppresses do-nothing update operations. See below for details.
+ </p>
+ <p>
+ <code class="literal">CREATE TRIGGER ... suppress_redundant_updates_trigger()</code>
+ </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
+ <a id="id-1.5.8.34.4.2.2.2.1.1.1" class="indexterm"></a>
+ <code class="function">tsvector_update_trigger</code> ( )
+ → <code class="returnvalue">trigger</code>
+ </p>
+ <p>
+ Automatically updates a <code class="type">tsvector</code> column from associated
+ plain-text document column(s). The text search configuration to use
+ is specified by name as a trigger argument. See
+ <a class="xref" href="textsearch-features.html#TEXTSEARCH-UPDATE-TRIGGERS" title="12.4.3. Triggers for Automatic Updates">Section 12.4.3</a> for details.
+ </p>
+ <p>
+ <code class="literal">CREATE TRIGGER ... tsvector_update_trigger(tsvcol, 'pg_catalog.swedish', title, body)</code>
+ </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
+ <a id="id-1.5.8.34.4.2.2.3.1.1.1" class="indexterm"></a>
+ <code class="function">tsvector_update_trigger_column</code> ( )
+ → <code class="returnvalue">trigger</code>
+ </p>
+ <p>
+ Automatically updates a <code class="type">tsvector</code> column from associated
+ plain-text document column(s). The text search configuration to use
+ is taken from a <code class="type">regconfig</code> column of the table. See
+ <a class="xref" href="textsearch-features.html#TEXTSEARCH-UPDATE-TRIGGERS" title="12.4.3. Triggers for Automatic Updates">Section 12.4.3</a> for details.
+ </p>
+ <p>
+ <code class="literal">CREATE TRIGGER ... tsvector_update_trigger_column(tsvcol, tsconfigcol, title, body)</code>
+ </p></td></tr></tbody></table></div></div><br class="table-break" /><p>
+ The <code class="function">suppress_redundant_updates_trigger</code> function,
+ when applied as a row-level <code class="literal">BEFORE UPDATE</code> trigger,
+ will prevent any update that does not actually change the data in the
+ row from taking place. This overrides the normal behavior which always
+ performs a physical row update
+ regardless of whether or not the data has changed. (This normal behavior
+ makes updates run faster, since no checking is required, and is also
+ useful in certain cases.)
+ </p><p>
+ Ideally, you should avoid running updates that don't actually
+ change the data in the record. Redundant updates can cost considerable
+ unnecessary time, especially if there are lots of indexes to alter,
+ and space in dead rows that will eventually have to be vacuumed.
+ However, detecting such situations in client code is not
+ always easy, or even possible, and writing expressions to detect
+ them can be error-prone. An alternative is to use
+ <code class="function">suppress_redundant_updates_trigger</code>, which will skip
+ updates that don't change the data. You should use this with care,
+ however. The trigger takes a small but non-trivial time for each record,
+ so if most of the records affected by updates do actually change,
+ use of this trigger will make updates run slower on average.
+ </p><p>
+ The <code class="function">suppress_redundant_updates_trigger</code> function can be
+ added to a table like this:
+</p><pre class="programlisting">
+CREATE TRIGGER z_min_update
+BEFORE UPDATE ON tablename
+FOR EACH ROW EXECUTE FUNCTION suppress_redundant_updates_trigger();
+</pre><p>
+ In most cases, you need to fire this trigger last for each row, so that
+ it does not override other triggers that might wish to alter the row.
+ Bearing in mind that triggers fire in name order, you would therefore
+ choose a trigger name that comes after the name of any other trigger
+ you might have on the table. (Hence the <span class="quote">“<span class="quote">z</span>”</span> prefix in the
+ example.)
+ </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="functions-admin.html" title="9.27. System Administration Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="functions.html" title="Chapter 9. Functions and Operators">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="functions-event-triggers.html" title="9.29. Event Trigger Functions">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.27. System Administration Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 9.29. Event Trigger Functions</td></tr></table></div></body></html> \ No newline at end of file
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