77 lines
4.9 KiB
HTML
77 lines
4.9 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<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))' />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Check constraints" />
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<meta name="abstract" content="You use check constraints to maintain limits on field values so that they conform to your database requirements." />
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<meta name="description" content="You use check constraints to maintain limits on field values so that they conform to your database requirements." />
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<meta name="DC.subject" content="constraint, check, check constraint" />
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<meta name="keywords" content="constraint, check, check constraint" />
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<meta name="DC.Relation" scheme="URI" content="rbaforzahfcoa.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rbaforzahfcon" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Check constraints</title>
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</head>
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<body id="rbaforzahfcon"><a name="rbaforzahfcon"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Check constraints</h1>
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<div><p>You use check constraints to maintain limits on field values so
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that they conform to your database requirements.</p>
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<p>Check constraints ensure data validity during insert or update operations
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by checking the data against a check constraint expression that you define.</p>
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<p>For example, you can create a check constraint on a field and define that
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the values that are inserted into the field must be between 1 and 100. If
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a value does not fall within the range, the insert or update operation against
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your database is not processed.</p>
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<div class="p">Check constraints are much like referential constraints in terms of their
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states: <ul><li><strong>Defined and enabled</strong>. The constraint definition has been added to
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the file, and the constraint will be enforced after the constraint is established.</li>
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<li><strong>Defined and disabled </strong>. The constraint definition has been added
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to the file, but the constraint will not be enforced.</li>
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<li><strong>Established and enabled</strong>. The constraint has been added to the file
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and all of the pieces of the file are there for enforcement.</li>
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<li><strong>Established and disabled</strong>. The constraint has been added to the
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file and all of the pieces of the file are there for enforcement, but the
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constraint will not be enforced.</li>
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</ul>
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</div>
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<p>A check constraint, like a referential constraint, can have a check pending
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status. If the data in any field violates the check constraint expression,
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then the constraint is in check pending status. For the insertion or update
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of a record, if the data violates the check constraint expression, then the
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insert or update operation is not allowed.</p>
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<div class="p">A check constraint that contains one or more Large Object (LOB) fields
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is restricted to a narrower range of operations than a check constraint without
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LOB fields. When the check constraint includes one or more LOB fields, the
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LOB fields can only be involved in direct comparisons to: <ul><li>Other LOB fields of the same type and same maximum length.</li>
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<li>Literal values.</li>
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<li>The null value.</li>
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</ul>
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</div>
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<p>Operations known as derived operations, such as the Substring or Concat
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operations, are not allowed against LOB fields in a check constraint. The
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diagnostic message CPD32E6 will be sent when you try to add a
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check constraint that attempts a derived operation against a LOB field.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbaforzahfcoa.htm" title="A constraint is a restriction or limitation placed on a file to ensure that the data in your database remains consistent as you add, change, and remove records. These topics describe how to use constraints to ensure data consistency.">Control the integrity of your database with constraints</a></div>
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</div>
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</div>
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</body>
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</html>
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