51 lines
3.1 KiB
HTML
51 lines
3.1 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="Unique constraints" />
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<meta name="abstract" content="Unique constraints act as controls in a database to ensure that rows are unique." />
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<meta name="description" content="Unique constraints act as controls in a database to ensure that rows are unique." />
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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="rbaforzahfcob" />
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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>Unique constraints</title>
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</head>
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<body id="rbaforzahfcob"><a name="rbaforzahfcob"><!-- --></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">Unique constraints</h1>
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<div><p>Unique constraints act as controls in a database to ensure that
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rows are unique. </p>
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<p>For example, you can specify a customer identification number as a unique
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constraint in your database. If anyone attempts to create a new customer with
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the same customer number, an error message is sent to the database administrator.</p>
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<p>Unique constraints identify a field or set of fields in a database file
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whose values must be unique across records in the file. The field must be
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in ascending order, and can be null-capable.</p>
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<p>A file can have multiple unique constraints, but you cannot duplicate unique
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constraints. The same key fields, regardless of order, constitute a duplicate
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constraint.</p>
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<p>A unique constraint can be used as the parent key when adding
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a referential constraint.</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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