259 lines
11 KiB
HTML
259 lines
11 KiB
HTML
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<title>Conversion rules for operations that combine strings</title>
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<a name="uuall"></a>
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<h2 id="uuall"><a href="rbafzmst02.htm#ToC_183">Conversion rules for operations that combine strings</a></h2>
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<p>The operations that combine strings are concatenation, UNION, UNION ALL,
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EXCEPT, and INTERSECT. (These rules also apply to the MAX, MIN, VALUE, COALESCE,
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IFNULL, and CONCAT scalar functions and CASE expressions.) In each case, the
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CCSID of the result is determined at bind time, and the execution of the operation
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may involve conversion of strings to the coded character set identified by
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that CCSID.</p>
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<p>The CCSID of the result is determined by the CCSIDs of the operands. The
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CCSIDs of the first two operands determine an intermediate result CCSID, this
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CCSID and the CCSID of the next operand determine a new intermediate result
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CCSID, and so on. The last intermediate result CCSID and the CCSID of the
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last operand determine the CCSID of the result string or column. For each
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pair of CCSIDs, the result CCSID is determined by the sequential application
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of the following rules: </p>
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<ul>
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<li>If the CCSIDs are equal, the result is that CCSID.</li>
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<li>If either CCSID is 65535, the result is 65535.<sup class="fn"><a id="wq252" name="wq252" href="rbafzmstuuall.htm#wq253">25</a></sup></li>
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<li>If one CCSID denotes data in an encoding scheme different from the other
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CCSID, the result is determined by the following table:</li></ul>
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<a name="wq254"></a>
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<table id="wq254" width="100%" summary="" border="1" frame="border" rules="all">
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<caption>Table 20. Selecting the Encoding Scheme of the Intermediate Result</caption>
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<thead valign="bottom">
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<tr>
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<th id="wq255" width="20%" rowspan="2" align="center" valign="bottom">First Operand</th>
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<th id="wq256" colspan="4" align="center" valign="bottom">Second
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Operand</th>
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</tr>
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<tr>
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<th id="wq257" width="20%" align="center" valign="bottom">SBCS Data</th>
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<th id="wq258" width="20%" align="center" valign="bottom">DBCS Data</th>
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<th id="wq259" width="20%" align="center" valign="bottom">Mixed Data</th>
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<th id="wq260" width="20%" align="center" valign="bottom">UTF-16 or UCS-2 Data</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr>
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<td align="left" valign="top" headers="wq255">SBCS Data</td>
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<td align="center" valign="top" headers="wq256 wq257">see below</td>
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<td align="center" valign="top" headers="wq256 wq258">second</td>
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<td align="center" valign="top" headers="wq256 wq259">second</td>
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<td align="center" valign="top" headers="wq256 wq260">second</td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq255">DBCS Data</td>
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<td align="center" valign="top" headers="wq256 wq257">first</td>
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<td align="center" valign="top" headers="wq256 wq258">see below</td>
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<td align="center" valign="top" headers="wq256 wq259">second</td>
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<td align="center" valign="top" headers="wq256 wq260">second</td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq255">Mixed Data</td>
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<td align="center" valign="top" headers="wq256 wq257">first</td>
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<td align="center" valign="top" headers="wq256 wq258">first</td>
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<td align="center" valign="top" headers="wq256 wq259">see below</td>
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<td align="center" valign="top" headers="wq256 wq260">second</td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq255">UTF-16 or UCS-2 Data</td>
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<td align="center" valign="top" headers="wq256 wq257">first</td>
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<td align="center" valign="top" headers="wq256 wq258">first</td>
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<td align="center" valign="top" headers="wq256 wq259">first</td>
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<td align="center" valign="top" headers="wq256 wq260">see below</td>
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</tr>
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</tbody>
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</table>
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<ul>
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<li>Otherwise, the resulting CCSID is determined by the following tables:</li></ul>
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<a name="wq261"></a>
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<table id="wq261" width="100%" summary="" border="1" frame="border" rules="all">
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<caption>Table 21. Selecting the CCSID of the Intermediate Result</caption>
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<thead valign="bottom">
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<tr>
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<th id="wq262" width="28%" rowspan="2" align="center" valign="bottom">First Operand</th>
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<th id="wq263" colspan="5" align="center" valign="bottom">Second
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Operand</th>
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</tr>
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<tr>
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<th id="wq264" width="14%" align="center" valign="bottom">Column Value</th>
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<th id="wq265" width="14%" align="center" valign="bottom">Derived Value</th>
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<th id="wq266" width="14%" align="center" valign="bottom">Constant</th>
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<th id="wq267" width="14%" align="center" valign="bottom">Special Register</th>
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<th id="wq268" width="13%" align="center" valign="bottom">Variable</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr>
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<td align="left" valign="top" headers="wq262">
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<div class="lines">Column Value<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq264">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq265">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq266">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq267">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq268">
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<div class="lines">first<br />
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</div></td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq262">
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<div class="lines">Derived Value<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq264">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq265">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq266">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq267">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq268">
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<div class="lines">first<br />
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</div></td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq262">
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<div class="lines">Constant<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq264">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq265">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq266">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq267">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq268">
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<div class="lines">first<br />
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</div></td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq262">
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<div class="lines">Special Register<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq264">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq265">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq266">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq267">
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<div class="lines">first<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq268">
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<div class="lines">first<br />
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</div></td>
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</tr>
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<tr>
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<td align="left" valign="top" headers="wq262">
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<div class="lines">Variable<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq264">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq265">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq266">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq267">
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<div class="lines">second<br />
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</div></td>
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<td align="center" valign="top" headers="wq263 wq268">
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<div class="lines">first<br />
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</div></td>
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</tr>
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</tbody>
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</table>
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<p>A variable containing data in a foreign encoding scheme is effectively
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converted to the native encoding scheme before it is used in any operation.
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The above rules are based on the assumption that this conversion has already
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occurred.</p>
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<p>Note that an intermediate result is considered to be a derived value operand.
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For example, assume COLA, COLB, and COLC are columns with CCSIDs 37, 278,
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and 500, respectively. The result CCSID of COLA CONCAT COLB CONCAT COLC is
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determined as follows: </p>
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<ol type="1">
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<li id="jstep1">
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<a name="jstep1"></a>The result CCSID of COLA CONCAT COLB is first determined to
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be 37 because both operands are columns, so the CCSID of the first operand
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is chosen.</li>
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<li>The result CCSID of "intermediate result" CONCAT COLC is determined
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to be 500, because the first operand is a derived value and the second operand
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is a column, so the CCSID of the second operand is chosen.</li></ol>
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<p>An operand of concatenation, or the result expression of the CASE expression,
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or the operands of the IN predicate, or the selected argument of the MAX,
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MIN, VALUE, COALESCE, IFNULL, or CONCAT scalar function is converted, if necessary,
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to the coded character set of the result string. Each string of an operand
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of UNION, UNION ALL, EXCEPT, or INTERSECT is converted, if necessary, to the
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coded character set of the result column. Character conversion is necessary
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only if all of the following are true: </p>
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<ul>
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<li>The CCSIDs are different.</li>
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<li>Neither CCSID is 65535.</li>
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<li>The string is neither null nor empty.</li>
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<li>The CCSID Conversion Selection Table (<a href="rbafzmstccseta.htm#conccsid">Coded character sets and CCSIDs</a>) indicates
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that conversion is necessary.</li></ul>
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<p>An error occurs if a character of a string cannot be converted or if the
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CCSID Conversion Selection Table is used but does not contain any information
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about the CCSID pair. A warning occurs if a character of a string is converted
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to the substitution character.</p>
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<hr /><div class="fnnum"><a id="wq253" name="wq253" href="rbafzmstuuall.htm#wq252">25</a>.</div>
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<div class="fntext">If either operand is
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a CLOB or DBCLOB, the resulting CCSID is the job default CCSID.</div>
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<br />
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<hr /><br />
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