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diff --git a/doc/src/sgml/html/sql-set-constraints.html b/doc/src/sgml/html/sql-set-constraints.html new file mode 100644 index 0000000..a52d504 --- /dev/null +++ b/doc/src/sgml/html/sql-set-constraints.html @@ -0,0 +1,71 @@ +<?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>SET CONSTRAINTS</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 Vsnapshot" /><link rel="prev" href="sql-set.html" title="SET" /><link rel="next" href="sql-set-role.html" title="SET ROLE" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">SET CONSTRAINTS</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-set.html" title="SET">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-set-role.html" title="SET ROLE">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-SET-CONSTRAINTS"><div class="titlepage"></div><a id="id-1.9.3.175.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">SET CONSTRAINTS</span></h2><p>SET CONSTRAINTS — set constraint check timing for the current transaction</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis"> +SET CONSTRAINTS { ALL | <em class="replaceable"><code>name</code></em> [, ...] } { DEFERRED | IMMEDIATE } +</pre></div><div class="refsect1" id="id-1.9.3.175.5"><h2>Description</h2><p> + <code class="command">SET CONSTRAINTS</code> sets the behavior of constraint + checking within the current transaction. <code class="literal">IMMEDIATE</code> + constraints are checked at the end of each + statement. <code class="literal">DEFERRED</code> constraints are not checked until + transaction commit. Each constraint has its own + <code class="literal">IMMEDIATE</code> or <code class="literal">DEFERRED</code> mode. + </p><p> + Upon creation, a constraint is given one of three + characteristics: <code class="literal">DEFERRABLE INITIALLY DEFERRED</code>, + <code class="literal">DEFERRABLE INITIALLY IMMEDIATE</code>, or + <code class="literal">NOT DEFERRABLE</code>. The third + class is always <code class="literal">IMMEDIATE</code> and is not affected by the + <code class="command">SET CONSTRAINTS</code> command. The first two classes start + every transaction in the indicated mode, but their behavior can be changed + within a transaction by <code class="command">SET CONSTRAINTS</code>. + </p><p> + <code class="command">SET CONSTRAINTS</code> with a list of constraint names changes + the mode of just those constraints (which must all be deferrable). Each + constraint name can be schema-qualified. The + current schema search path is used to find the first matching name if + no schema name is specified. <code class="command">SET CONSTRAINTS ALL</code> + changes the mode of all deferrable constraints. + </p><p> + When <code class="command">SET CONSTRAINTS</code> changes the mode of a constraint + from <code class="literal">DEFERRED</code> + to <code class="literal">IMMEDIATE</code>, the new mode takes effect + retroactively: any outstanding data modifications that would have + been checked at the end of the transaction are instead checked during the + execution of the <code class="command">SET CONSTRAINTS</code> command. + If any such constraint is violated, the <code class="command">SET CONSTRAINTS</code> + fails (and does not change the constraint mode). Thus, <code class="command">SET + CONSTRAINTS</code> can be used to force checking of constraints to + occur at a specific point in a transaction. + </p><p> + Currently, only <code class="literal">UNIQUE</code>, <code class="literal">PRIMARY KEY</code>, + <code class="literal">REFERENCES</code> (foreign key), and <code class="literal">EXCLUDE</code> + constraints are affected by this setting. + <code class="literal">NOT NULL</code> and <code class="literal">CHECK</code> constraints are + always checked immediately when a row is inserted or modified + (<span class="emphasis"><em>not</em></span> at the end of the statement). + Uniqueness and exclusion constraints that have not been declared + <code class="literal">DEFERRABLE</code> are also checked immediately. + </p><p> + The firing of triggers that are declared as <span class="quote">“<span class="quote">constraint triggers</span>”</span> + is also controlled by this setting — they fire at the same time + that the associated constraint should be checked. + </p></div><div class="refsect1" id="id-1.9.3.175.6"><h2>Notes</h2><p> + Because <span class="productname">PostgreSQL</span> does not require constraint + names to be unique within a schema (but only per-table), it is possible + that there is more than one match for a specified constraint name. + In this case <code class="command">SET CONSTRAINTS</code> will act on all matches. + For a non-schema-qualified name, once a match or matches have been found in + some schema in the search path, schemas appearing later in the path are not + searched. + </p><p> + This command only alters the behavior of constraints within the + current transaction. Issuing this outside of a transaction block + emits a warning and otherwise has no effect. + </p></div><div class="refsect1" id="id-1.9.3.175.7"><h2>Compatibility</h2><p> + This command complies with the behavior defined in the SQL + standard, except for the limitation that, in + <span class="productname">PostgreSQL</span>, it does not apply to + <code class="literal">NOT NULL</code> and <code class="literal">CHECK</code> constraints. + Also, <span class="productname">PostgreSQL</span> checks non-deferrable + uniqueness constraints immediately, not at end of statement as the + standard would suggest. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-set.html" title="SET">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-set-role.html" title="SET ROLE">Next</a></td></tr><tr><td width="40%" align="left" valign="top">SET </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> SET ROLE</td></tr></table></div></body></html>
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