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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/sql-set-constraints.html

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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 V1.79.1" /><link rel="prev" href="sql-set.html" title="SET" /><link rel="next" href="sql-set-role.html" title="SET ROLE" /></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">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 12.4 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></hr></div><div class="refentry" id="SQL-SET-CONSTRAINTS"><div class="titlepage"></div><a id="id-1.9.3.174.1" 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">

  3. SET CONSTRAINTS { ALL | <em class="replaceable"><code>name</code></em> [, ...] } { DEFERRED | IMMEDIATE }

  4. </pre></div><div class="refsect1" id="id-1.9.3.174.5"><h2>Description</h2><p>

  5.    <code class="command">SET CONSTRAINTS</code> sets the behavior of constraint

  6.    checking within the current transaction. <code class="literal">IMMEDIATE</code>

  7.    constraints are checked at the end of each

  8.    statement. <code class="literal">DEFERRED</code> constraints are not checked until

  9.    transaction commit.  Each constraint has its own

  10.    <code class="literal">IMMEDIATE</code> or <code class="literal">DEFERRED</code> mode.

  11.   </p><p>

  12.    Upon creation, a constraint is given one of three

  13.    characteristics: <code class="literal">DEFERRABLE INITIALLY DEFERRED</code>,

  14.    <code class="literal">DEFERRABLE INITIALLY IMMEDIATE</code>, or

  15.    <code class="literal">NOT DEFERRABLE</code>. The third

  16.    class is always <code class="literal">IMMEDIATE</code> and is not affected by the

  17.    <code class="command">SET CONSTRAINTS</code> command.  The first two classes start

  18.    every transaction in the indicated mode, but their behavior can be changed

  19.    within a transaction by <code class="command">SET CONSTRAINTS</code>.

  20.   </p><p>

  21.    <code class="command">SET CONSTRAINTS</code> with a list of constraint names changes

  22.    the mode of just those constraints (which must all be deferrable).  Each

  23.    constraint name can be schema-qualified.  The

  24.    current schema search path is used to find the first matching name if

  25.    no schema name is specified.  <code class="command">SET CONSTRAINTS ALL</code>

  26.    changes the mode of all deferrable constraints.

  27.   </p><p>

  28.    When <code class="command">SET CONSTRAINTS</code> changes the mode of a constraint

  29.    from <code class="literal">DEFERRED</code>

  30.    to <code class="literal">IMMEDIATE</code>, the new mode takes effect

  31.    retroactively: any outstanding data modifications that would have

  32.    been checked at the end of the transaction are instead checked during the

  33.    execution of the <code class="command">SET CONSTRAINTS</code> command.

  34.    If any such constraint is violated, the <code class="command">SET CONSTRAINTS</code>

  35.    fails (and does not change the constraint mode).  Thus, <code class="command">SET

  36.    CONSTRAINTS</code> can be used to force checking of constraints to

  37.    occur at a specific point in a transaction.

  38.   </p><p>

  39.    Currently, only <code class="literal">UNIQUE</code>, <code class="literal">PRIMARY KEY</code>,

  40.    <code class="literal">REFERENCES</code> (foreign key), and <code class="literal">EXCLUDE</code>

  41.    constraints are affected by this setting.

  42.    <code class="literal">NOT NULL</code> and <code class="literal">CHECK</code> constraints are

  43.    always checked immediately when a row is inserted or modified

  44.    (<span class="emphasis"><em>not</em></span> at the end of the statement).

  45.    Uniqueness and exclusion constraints that have not been declared

  46.    <code class="literal">DEFERRABLE</code> are also checked immediately.

  47.   </p><p>

  48.    The firing of triggers that are declared as <span class="quote">“<span class="quote">constraint triggers</span>”</span>

  49.    is also controlled by this setting — they fire at the same time

  50.    that the associated constraint should be checked.

  51.   </p></div><div class="refsect1" id="id-1.9.3.174.6"><h2>Notes</h2><p>

  52.    Because <span class="productname">PostgreSQL</span> does not require constraint

  53.    names to be unique within a schema (but only per-table), it is possible

  54.    that there is more than one match for a specified constraint name.

  55.    In this case <code class="command">SET CONSTRAINTS</code> will act on all matches.

  56.    For a non-schema-qualified name, once a match or matches have been found in

  57.    some schema in the search path, schemas appearing later in the path are not

  58.    searched.

  59.   </p><p>

  60.    This command only alters the behavior of constraints within the

  61.    current transaction.  Issuing this outside of a transaction block

  62.    emits a warning and otherwise has no effect.

  63.   </p></div><div class="refsect1" id="id-1.9.3.174.7"><h2>Compatibility</h2><p>

  64.    This command complies with the behavior defined in the SQL

  65.    standard, except for the limitation that, in

  66.    <span class="productname">PostgreSQL</span>, it does not apply to

  67.    <code class="literal">NOT NULL</code> and <code class="literal">CHECK</code> constraints.

  68.    Also, <span class="productname">PostgreSQL</span> checks non-deferrable

  69.    uniqueness constraints immediately, not at end of statement as the

  70.    standard would suggest.

  71.   </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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-set-role.html">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">Home</a></td><td width="40%" align="right" valign="top"> SET ROLE</td></tr></table></div></body></html>
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