1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
|
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>SET CONSTRAINTS</title>
<link rel="stylesheet" href="stylesheet.css" type="text/css">
<link rev="made" href="pgsql-docs@postgresql.org">
<meta name="generator" content="DocBook XSL Stylesheets V1.70.0">
<link rel="start" href="index.html" title="PostgreSQL 8.1.4 Documentation">
<link rel="up" href="sql-commands.html" title="SQL Commands">
<link rel="prev" href="sql-set.html" title="SET">
<link rel="next" href="sql-set-role.html" title="SET ROLE">
<link rel="copyright" href="ln-legalnotice.html" title="Legal Notice">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="sql-set-constraints"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>SET CONSTRAINTS — set constraint checking modes for the current transaction</p>
</div>
<a name="id787745"></a><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" lang="en">
<a name="id787770"></a><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). If
there are multiple constraints matching any given name, all are affected.
<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 foreign key constraints are affected by this
setting. Check and unique constraints are always effectively
not deferrable.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id787936"></a><h2>Notes</h2>
<p> This command only alters the behavior of constraints within the
current transaction. Thus, if you execute this command outside of a
transaction block
(<code class="command">BEGIN</code>/<code class="command">COMMIT</code> pair), it will
not appear to have any effect.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id787958"></a><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 only applies to
foreign-key constraints.
</p>
<p> The SQL standard says that constraint names appearing in <code class="command">SET
CONSTRAINTS</code> can be schema-qualified. This is not yet
supported by <span class="productname">PostgreSQL</span>: the names must
be unqualified, and all constraints matching the command will be
affected no matter which schema they are in.
</p>
</div>
</div></body>
</html>
|
