76 lines
4.6 KiB
HTML
76 lines
4.6 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
|
||
|
|
<meta name="DC.Type" content="reference" />
|
||
|
|
<meta name="DC.Title" content="Add and use check constraints" />
|
||
|
|
<meta name="abstract" content="A check constraint assures the validity of data during insert and update operations by limiting the allowable values in a column or group of columns." />
|
||
|
|
<meta name="description" content="A check constraint assures the validity of data during insert and update operations by limiting the allowable values in a column or group of columns." />
|
||
|
|
<meta name="DC.subject" content="examples, check constraints, CREATE TABLE statement, ALTER TABLE statement, constraint, check, adding, using" />
|
||
|
|
<meta name="keywords" content="examples, check constraints, CREATE TABLE statement, ALTER TABLE statement, constraint, check, adding, using" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafymovnow.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="../db2/rbafzmstatabl.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="../db2/rbafzmsthctabl.htm" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="rbafycheckcon" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>Add and use check constraints</title>
|
||
|
|
</head>
|
||
|
|
<body id="rbafycheckcon"><a name="rbafycheckcon"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Add and use check constraints</h1>
|
||
|
|
<div><p>A <em>check constraint</em> assures the validity of data during insert
|
||
|
|
and update operations by limiting the allowable values in a column
|
||
|
|
or group of columns.</p>
|
||
|
|
<div class="section"><p>Use the SQL CREATE TABLE and ALTER TABLE statements to add or
|
||
|
|
drop check constraints.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>In this example, the following statement creates a table with
|
||
|
|
three columns and a check constraint over COL2 that limits the values allowed
|
||
|
|
in that column to positive integers: </p>
|
||
|
|
<pre><strong>CREATE TABLE</strong> T1 (COL1 <strong>INT</strong>, COL2 <strong>INT CHECK</strong> (COL2>0), COL3 <strong>INT</strong>)</pre>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Given this table, the following statement:</p>
|
||
|
|
<pre><strong>INSERT INTO</strong> T1 <strong>VALUES</strong> (-1, -1, -1)</pre>
|
||
|
|
<p>fails
|
||
|
|
because the value to be inserted into COL2 does not meet the check constraint;
|
||
|
|
that is, -1 is not greater than 0.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>The following statement is successful:</p>
|
||
|
|
</div>
|
||
|
|
<div class="example"> <pre><strong>INSERT INTO</strong> T1 <strong>VALUES</strong> (1, 1, 1)</pre>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Once that row is inserted, the following statement fails: </p>
|
||
|
|
<pre><strong>ALTER TABLE</strong> T1 <strong>ADD CONSTRAINT</strong> C1 <strong>CHECK</strong> (COL1=1 <strong>AND</strong> COL1<COL2)</pre>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>This ALTER TABLE statement attempts to add a second check constraint
|
||
|
|
that limits the value allowed in COL1 to 1 and also effectively rules that
|
||
|
|
values in COL2 be greater than 1. This constraint is not allowed because the
|
||
|
|
second part of the constraint is not met by the existing data (the value of
|
||
|
|
'1' in COL2 is not less than the value of '1' in COL1).</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafymovnow.htm" title="DB2 UDB for iSeries supports unique, referential, and check constraints.">Constraints</a></div>
|
||
|
|
</div>
|
||
|
|
<div class="relinfo"><strong>Related information</strong><br />
|
||
|
|
<div><a href="../db2/rbafzmstatabl.htm">ALTER TABLE statement</a></div>
|
||
|
|
<div><a href="../db2/rbafzmsthctabl.htm">CREATE TABLE statement</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|