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<!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>44.6. PL/Perl Triggers</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="[email protected]" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plperl-trusted.html" title="44.5. Trusted and Untrusted PL/Perl" /><link rel="next" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.6. PL/Perl Triggers</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl-trusted.html" title="44.5. Trusted and Untrusted PL/Perl">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Perl - Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 10.23 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPERL-TRIGGERS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.6. PL/Perl Triggers</h2></div></div></div><p> PL/Perl can be used to write trigger functions. In a trigger function,
the hash reference <code class="varname">$_TD</code> contains information about the
current trigger event. <code class="varname">$_TD</code> is a global variable,
which gets a separate local value for each invocation of the trigger.
The fields of the <code class="varname">$_TD</code> hash reference are:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">$_TD->{new}{foo}</code></span></dt><dd><p> <code class="literal">NEW</code> value of column <code class="literal">foo</code>
</p></dd><dt><span class="term"><code class="literal">$_TD->{old}{foo}</code></span></dt><dd><p> <code class="literal">OLD</code> value of column <code class="literal">foo</code>
</p></dd><dt><span class="term"><code class="literal">$_TD->{name}</code></span></dt><dd><p> Name of the trigger being called
</p></dd><dt><span class="term"><code class="literal">$_TD->{event}</code></span></dt><dd><p> Trigger event: <code class="literal">INSERT</code>, <code class="literal">UPDATE</code>,
<code class="literal">DELETE</code>, <code class="literal">TRUNCATE</code>, or <code class="literal">UNKNOWN</code>
</p></dd><dt><span class="term"><code class="literal">$_TD->{when}</code></span></dt><dd><p> When the trigger was called: <code class="literal">BEFORE</code>,
<code class="literal">AFTER</code>, <code class="literal">INSTEAD OF</code>, or
<code class="literal">UNKNOWN</code>
</p></dd><dt><span class="term"><code class="literal">$_TD->{level}</code></span></dt><dd><p> The trigger level: <code class="literal">ROW</code>, <code class="literal">STATEMENT</code>, or <code class="literal">UNKNOWN</code>
</p></dd><dt><span class="term"><code class="literal">$_TD->{relid}</code></span></dt><dd><p> OID of the table on which the trigger fired
</p></dd><dt><span class="term"><code class="literal">$_TD->{table_name}</code></span></dt><dd><p> Name of the table on which the trigger fired
</p></dd><dt><span class="term"><code class="literal">$_TD->{relname}</code></span></dt><dd><p> Name of the table on which the trigger fired. This has been deprecated,
and could be removed in a future release.
Please use $_TD->{table_name} instead.
</p></dd><dt><span class="term"><code class="literal">$_TD->{table_schema}</code></span></dt><dd><p> Name of the schema in which the table on which the trigger fired, is
</p></dd><dt><span class="term"><code class="literal">$_TD->{argc}</code></span></dt><dd><p> Number of arguments of the trigger function
</p></dd><dt><span class="term"><code class="literal">@{$_TD->{args}}</code></span></dt><dd><p> Arguments of the trigger function. Does not exist if <code class="literal">$_TD->{argc}</code> is 0.
</p></dd></dl></div><p>
</p><p> Row-level triggers can return one of the following:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">return;</code></span></dt><dd><p> Execute the operation
</p></dd><dt><span class="term"><code class="literal">"SKIP"</code></span></dt><dd><p> Don't execute the operation
</p></dd><dt><span class="term"><code class="literal">"MODIFY"</code></span></dt><dd><p> Indicates that the <code class="literal">NEW</code> row was modified by
the trigger function
</p></dd></dl></div><p>
</p><p> Here is an example of a trigger function, illustrating some of the
above:
</p><pre class="programlisting">CREATE TABLE test (
i int,
v varchar
);
CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
if (($_TD->{new}{i} >= 100) || ($_TD->{new}{i} <= 0)) {
return "SKIP"; # skip INSERT/UPDATE command
} elsif ($_TD->{new}{v} ne "immortal") {
$_TD->{new}{v} .= "(modified by trigger)";
return "MODIFY"; # modify row and execute INSERT/UPDATE command
} else {
return; # execute INSERT/UPDATE command
}
$$ LANGUAGE plperl;
CREATE TRIGGER test_valid_id_trig
BEFORE INSERT OR UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE valid_id();</pre><p>
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