80 lines
5.3 KiB
HTML
80 lines
5.3 KiB
HTML
<?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="DC.Type" content="reference" />
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<meta name="DC.Title" content="WITH LOCAL CHECK OPTION" />
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<meta name="abstract" content="The WITH LOCAL CHECK OPTION clause is identical to the WITH CASCADED CHECK OPTION clause except that you can update a row so that it no longer can be retrieved through the view. This can only happen when the view is directly or indirectly dependent on a view that was defined with no WITH CHECK OPTION clause." />
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<meta name="description" content="The WITH LOCAL CHECK OPTION clause is identical to the WITH CASCADED CHECK OPTION clause except that you can update a row so that it no longer can be retrieved through the view. This can only happen when the view is directly or indirectly dependent on a view that was defined with no WITH CHECK OPTION clause." />
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<meta name="DC.subject" content="CREATE VIEW statement, WITH LOCAL CHECK OPTION, view, WITH LOCAL CHECK" />
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<meta name="keywords" content="CREATE VIEW statement, WITH LOCAL CHECK OPTION, view, WITH LOCAL CHECK" />
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<meta name="DC.Relation" scheme="URI" content="rbafywcohdg.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="rbafywithlocalcheck" />
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<meta name="DC.Language" content="en-us" />
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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>WITH LOCAL CHECK OPTION</title>
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</head>
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<body id="rbafywithlocalcheck"><a name="rbafywithlocalcheck"><!-- --></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">WITH LOCAL CHECK OPTION</h1>
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<div><p>The WITH LOCAL CHECK OPTION clause is identical to the WITH CASCADED
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CHECK OPTION clause except that you can update a row so that it no longer
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can be retrieved through the view. This can only happen when the view is directly
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or indirectly dependent on a view that was defined with no WITH CHECK OPTION
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clause.</p>
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<div class="section"><p>For example, consider the same updatable view used in the previous
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example:</p>
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<pre> <strong>CREATE VIEW</strong> V1 <strong>AS SELECT</strong> COL1
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<strong>FROM</strong> T1 <strong>WHERE</strong> COL1 > 10</pre>
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</div>
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<div class="section"><p>Create second view over V1, this time specifying WITH LOCAL CHECK
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OPTION:</p>
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<pre> <strong>CREATE VIEW</strong> V2 <strong>AS SELECT</strong> COL1
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<strong>FROM</strong> V1 <strong>WITH LOCAL CHECK OPTION</strong></pre>
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</div>
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<div class="section"><p>The same INSERT statement that failed in the previous CASCADED
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CHECK OPTION example succeeds now because V2 does not have any search conditions,
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and the search conditions of V1 do not need to be checked since V1 does not
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specify a check option.</p>
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<pre> <strong>INSERT INTO</strong> V2 <strong>VALUES</strong> (5)</pre>
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</div>
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<div class="section"><p>Consider one more view created over V2:</p>
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<pre> <strong>CREATE VIEW</strong> V3 <strong>AS SELECT</strong> COL1
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<strong>FROM</strong> V2 <strong>WHERE</strong> COL1 < 100</pre>
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</div>
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<div class="section"><p>The following INSERT is successful again because the search condition
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on V1 is not checked due to the WITH LOCAL CHECK OPTION on V2, versus the
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WITH CASCADED CHECK OPTION in the previous example. </p>
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<pre> <strong>INSERT INTO</strong> V3 <strong>VALUES</strong> (5)</pre>
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</div>
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<div class="section"><p>The difference between LOCAL and CASCADED CHECK OPTION lies in
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how many of the dependent views' search conditions are checked when a row
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is inserted or updated. </p>
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<ul><li>WITH LOCAL CHECK OPTION specifies that the search conditions of only those
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dependent views that have the WITH LOCAL CHECK OPTION or WITH CASCADED CHECK
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OPTION are checked when a row is inserted or updated.</li>
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<li>WITH CASCADED CHECK OPTION specifies that the search conditions of all
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dependent views are checked when a row is inserted or updated.</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 class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafywcohdg.htm" title="WITH CHECK OPTION is an optional clause on the CREATE VIEW statement that specifies the level of checking to be done when inserting or updating data through a view. If the option is specified, every row that is inserted or updated through the view must conform to the definition of that view.">WITH CHECK OPTION on a View</a></div>
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</div>
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</div>
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</body>
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</html> |