76 lines
5.2 KiB
HTML
76 lines
5.2 KiB
HTML
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Constraints" />
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<meta name="abstract" content="DB2 UDB for iSeries supports unique, referential, and check constraints." />
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<meta name="description" content="DB2 UDB for iSeries supports unique, referential, and check constraints." />
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<meta name="DC.subject" content="constraint, data integrity, Edit Rebuild of Access Paths (EDTRBDAP) command, command (CL), Edit Rebuild of Access Paths (EDTRBDAP), EDTRBDAP (Edit Rebuild of Access Paths), check pending, data integrity, Edit Check Pending Constraints (EDTCPCST) command, Edit Check Pending Constraints (EDTCPCST), EDTCPCST (Edit Check Pending Constraints)" />
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<meta name="DC.Relation" scheme="URI" content="rbafycheckcon.htm" />
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<title>Constraints</title>
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<body id="rbafymovnow"><a name="rbafymovnow"><!-- --></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">Constraints</h1>
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<div><p><span class="keyword">DB2<sup>®</sup> UDB for iSeries™</span> supports
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unique, referential, and check constraints.</p>
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<div class="section"><p>A unique constraint is a rule that guarantees that the values
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of a key are unique. A referential constraint is a rule that all non-null
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values of foreign keys in a dependent table have a corresponding parent key
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in a parent table. A check constraint is a rule that limits the values allowed
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in a column or group of columns.</p>
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</div>
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<div class="section"><div class="p"><span class="keyword">DB2 UDB for iSeries</span> will enforce
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the validity of the constraint during any DML (data manipulation language)
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statement. Certain operations (such as restore of the dependent table), however,
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cause the validity of the constraint to be unknown. In this case, DML statements
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may be prevented until <span class="keyword">DB2 UDB for iSeries</span> has
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verified the validity of the constraint. <ul><li>Unique constraints are implemented with indexes. If an index that implements
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a unique constraint is invalid, the Edit Rebuild of Access Paths (EDTRBDAP)
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command can be used to display any indexes that currently require rebuild.</li>
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<li>If <span class="keyword">DB2 UDB for iSeries</span> does not currently
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know whether a referential constraint or check constraint is valid, the constraint
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is considered to be in a check pending state. The Edit Check Pending Constraints
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(EDTCPCST) command can be used to display any indexes that currently require
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rebuild.</li>
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</ul>
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</div>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rbafycheckcon.htm">Add and use check constraints</a></strong><br />
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A <em>check constraint</em> assures the validity of data during insert
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and update operations by limiting the allowable values in a column
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or group of columns.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafydataintex.htm" title="Data integrity protects data from being destroyed or changed by unauthorized persons, system operation or hardware failures (such as physical damage to a disk), programming errors, interruptions before a job is completed (such as a power failure), or interference from running applications at the same time (such as serialization problems).">Data integrity</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rbafyconstex.htm" title="Constraints are rules enforced by the database manager.">Constraints</a></div>
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</div>
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</div>
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