140 lines
8.3 KiB
HTML
140 lines
8.3 KiB
HTML
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" 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.language" scheme="rfc1766" content="en-us" />
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<meta name="dc.date" scheme="iso8601" content="2005-09-19" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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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="keywords" content="CASE statement, SQL-control-statement,
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SQL statements" />
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<title>CASE statement</title>
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<link rel="stylesheet" type="text/css" href="ibmidwb.css" />
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<link rel="stylesheet" type="text/css" href="ic.css" />
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</head>
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<body>
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<a id="Top_Of_Page" name="Top_Of_Page"></a><!-- Java sync-link -->
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<script language = "Javascript" src = "../rzahg/synch.js" type="text/javascript"></script>
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<a name="casestmt"></a>
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<h2 id="casestmt"><a href="rbafzmst02.htm#ToC_1420">CASE statement</a></h2><a id="idx3337" name="idx3337"></a><a id="idx3338" name="idx3338"></a>
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<p>The CASE statement selects an execution path based on multiple conditions.</p>
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<a name="wq1860"></a>
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<h3 id="wq1860"><a href="rbafzmst02.htm#ToC_1421">Syntax</a></h3>
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<a href="rbafzmstcasestmt.htm#synccase"><img src="c.gif" alt="Click to skip syntax diagram" /></a>
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<pre class="cgraphic"><span><img src="c.gif" alt="Read syntax diagram" longdesc="rbafzmstsyn409.htm"
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border="0" /></span><a href="#skipsyn-408"><img src="c.gif" alt="Skip visual syntax diagram"
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border="0" /></a>>>-+--------+--CASE--+-<span class="italic">simple-when-clause</span>---+------------------->
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'-<span class="italic">label:</span>-' '-<span class="italic">searched-when-clause</span>-'
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>--+-------------+--END CASE-----------------------------------><
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'-<span class="italic">else-clause</span>-'
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simple-when-clause:
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|--<span class="italic">expression</span>--------------------------------------------------->
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.---------------------------------------------------------.
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| .-----------------------------. |
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V V | |
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>----WHEN--<span class="italic">expression</span>--THEN----<span class="italic">SQL-procedure-statement</span>-- ;-+-+--|
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searched-when-clause:
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.---------------------------------------------------------------.
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| .-----------------------------. |
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V V | |
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|----WHEN--<span class="italic">search-condition</span>--THEN----<span class="italic">SQL-procedure-statement</span>-- ;-+-+--|
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else-clause:
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.-----------------------------.
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V |
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|--ELSE----<span class="italic">SQL-procedure-statement</span>-- ;-+------------------------|
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</pre>
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<a name="skipsyn-408" id="skipsyn-408"></a>
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<a name="synccase"></a>
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<h3 id="synccase"><a href="rbafzmst02.htm#ToC_1422">Description</a></h3>
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<dl class="parml">
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<dt class="bold"><span class="italic">label</span></dt>
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<dd>Specifies the label for the CASE statement. The label name
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cannot be the same as another label within the same scope. For more information,
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see <a href="rbafzmstsqlprocstmt.htm#psscope">Labels</a>.
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</dd>
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<dt class="bold"><span class="italic">simple-when-clause</span></dt>
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<dd>The value of the <var class="pv">expression</var> prior to the first WHEN keyword
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is tested for equality with the value of each <var class="pv">expression</var> that follows
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the WHEN keyword. If the comparison is true, the THEN statement is executed.
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If the result is unknown or false, processing continues to the next comparison.
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If the result does not match any of the comparisons, and an ELSE clause is
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present, the statements in the ELSE clause are processed.
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</dd>
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<dt class="bold"><span class="italic">searched-when-clause</span></dt>
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<dd>The <var class="pv">search-condition</var> following the WHEN keyword is evaluated.
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If it evaluates to true, the statements in the associated THEN clause are
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processed. If it evaluates to false, or unknown, the next <var class="pv">search-condition</var> is evaluated. If no <var class="pv">search-condition</var> evaluates to true and
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an ELSE clause is present, the statements in the ELSE clause are processed.
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</dd>
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<dt class="bold"><span class="italic">else-clause</span></dt>
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<dd>If none of the conditions specified in the <span class="italic">simple-when-clause</span> or <span class="italic">searched-when-clause</span> are true, then the statements
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in the <span class="italic">else-clause</span> are executed.
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<p>If none of the
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conditions specified in the WHEN are true, and an ELSE clause is not specified,
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an error is issued at runtime, and the execution of the CASE statement is
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terminated (SQLSTATE 20000).</p>
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</dd>
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<dt class="bold"><span class="italic">SQL-procedure-statement</span></dt>
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<dd>Specifies a statement that should be executed. See <a href="rbafzmstsqlprocstmt.htm#sqlprocstmt">SQL-procedure-statement</a>.
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</dd>
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</dl>
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<a name="wq1861"></a>
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<h3 id="wq1861"><a href="rbafzmst02.htm#ToC_1423">Notes</a></h3>
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<p><span class="bold">Nesting of CASE statements:</span> CASE statements that
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use a <span class="italic">simple-when-clause</span> can be nested up to three
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levels. CASE statements that use a <span class="italic">searched-when-clause</span> have no limit to the number of nesting levels.</p>
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<a name="wq1862"></a>
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<h3 id="wq1862"><a href="rbafzmst02.htm#ToC_1424">Examples</a></h3>
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<p><span class="italic">Example 1:</span> Depending on the value of SQL variable
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v_workdept, update column DEPTNAME in table DEPARTMENT with the appropriate
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name.</p>
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<p>The following example shows how to do this using the syntax for a <span class="italic">simple-when-clause</span>.</p>
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<pre class="xmp"> <span class="bold">CASE</span> v_workdept
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<span class="bold">WHEN</span> 'A00'
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<span class="bold">THEN UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 1';
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<span class="bold">WHEN</span> 'B01'
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<span class="bold">THEN UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 2';
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<span class="bold">ELSE UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 3';
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<span class="bold">END CASE</span> </pre>
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<p><span class="italic">Example 2:</span> The following example shows how to do
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this using the syntax for a <span class="italic">searched-when-clause</span>:</p>
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<pre class="xmp"> <span class="bold">CASE</span>
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<span class="bold">WHEN</span> v_workdept = 'A00'
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<span class="bold">THEN UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 1';
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<span class="bold">WHEN</span> v_workdept = 'B01'
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<span class="bold">THEN UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 2';
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<span class="bold">ELSE UPDATE</span> department <span class="bold">SET</span>
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deptname = 'DATA ACCESS 3';
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<span class="bold">END CASE</span></pre>
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<hr /><br />
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[ <a href="#Top_Of_Page">Top of Page</a> | <a href="rbafzmstcallstmt.htm">Previous Page</a> | <a href="rbafzmstcompoundstmt.htm">Next Page</a> | <a href="rbafzmst02.htm#wq1">Contents</a> |
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