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<title>Ensuring Data Integrity in Tables</title>
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<p><a id="BABJFCCE" name="BABJFCCE"></a><a id="TDDDG32200" name="TDDDG32200"></a></p>
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<h1>Ensuring Data Integrity in Tables</h1>
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<p><a id="sthref201" name="sthref201"></a><a id="sthref202" name="sthref202"></a>To ensure that the data in your tables satisfies the business rules that your application models, you can use constraints, application logic, or both.</p>
<p><a id="sthref203" name="sthref203"></a><span class="bold">Constraints</span> restrict the values that columns can have. Trying to change the data in a way that violates a constraint causes an error and rolls back the change. Trying to add a constraint to a populated table causes an error if existing data violates the constraint.</p>
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<p class="notep1">Tip:</p>
Wherever possible, use constraints instead of application logic. Oracle Database checks that all data obeys constraints much faster than application logic can.</td>
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<p><a id="sthref204" name="sthref204"></a>Constraints can be enabled and disabled. By default, they are created in the enabled state.</p>
<p>This section contains:</p>
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<p><a href="tdddg_objects009.htm#BABIBCDA">About Constraint Types</a></p>
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<p><a href="tdddg_objects010.htm#CIHHFGCB">Tutorial: Adding Constraints to Existing Tables</a></p>
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<h2>Related Topics</h2>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=CNCPT122','newWindow').focus()"><span class="italic">Oracle Database Concepts</span></a></p>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=SQLRF01111','newWindow').focus()"><span class="italic">Oracle Database SQL Language Reference</span></a></p>
<p><a href="tdddg_deploying013.htm#BABBJBEJ">Installing the Sample Application</a></p>
<p><a href="tdddg_objects003.htm#BABEBEJF">Creating and Managing Tables</a></p>
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