57 lines
4.0 KiB
HTML
57 lines
4.0 KiB
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<meta name="abstract" content="When you use a correlated subquery in a DELETE statement, the correlation name represents the row you delete. SQL evaluates the correlated subquery once for each row in the table named in the DELETE statement to decide whether to delete the row." />
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<title>Example: Correlated subqueries in a DELETE statement</title>
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<body id="rbafyexsub5"><a name="rbafyexsub5"><!-- --></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">Example: Correlated subqueries in a DELETE statement</h1>
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<div><p>When you use a correlated subquery in a DELETE statement, the correlation
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name represents the row you delete. SQL evaluates the correlated subquery
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once for each row in the table named in the DELETE statement to decide whether
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to delete the row.</p>
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<div class="section"><p>Suppose a row in the CORPDATA.PROJECT table was deleted. Rows
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related to the deleted project in the CORPDATA.EMPPROJACT table must also
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be deleted. To do this, you can use: </p>
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<pre> <strong>DELETE FROM</strong> CORPDATA.EMPPROJACT X
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<strong>WHERE NOT EXISTS</strong>
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(<strong>SELECT</strong> *
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<strong>FROM</strong> CORPDATA.PROJECT
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<strong>WHERE</strong> PROJNO = X.PROJNO)</pre>
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</div>
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<div class="section"><p>SQL determines, for each row in the CORPDATA.EMP_ACT table, whether
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a row with the same project number exists in the CORPDATA.PROJECT table. If
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not, the CORPDATA.EMP_ACT row is deleted.</p>
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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="rbafycorrs.htm" title="You can write a subquery that SQL might need to re-evaluate as it examines each new row (WHERE clause) or group of rows (HAVING clause) in the outer-level SELECT. This is called a correlated subquery.">Correlated subqueries</a></div>
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