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copied!<p>You would have to define a user-defined aggregate to do this. That has four parts - four functions (search for <a href="https://www.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.sqls.doc/ids_sqs_0358.htm" rel="nofollow noreferrer">CREATE AGGREGATE</a> in the <a href="http://www-01.ibm.com/support/knowledgecenter/SSGU8G_12.1.0/com.ibm.welcome.doc/welcome.htm" rel="nofollow noreferrer">IDS 12.10 Info Centre</a>):</p> <ol> <li>Initializer (INIT)</li> <li>Iterator (ITER)</li> <li>Combine (COMBINE)</li> <li>Finalizer (FINAL)</li> </ol> <p>That's the official terminology in capitals, and it is moderately intuitive. Think of calculating an average.</p> <ol> <li>Initializer: set sum = 0; N = 0</li> <li>Iterator: set sum += x; N++</li> <li>Combiner: set sum = sum1 + sum2; set N = N1 + N2</li> <li>Finalizer: result = sum / N -- with N=0 (zero-divide) checks</li> </ol> <p>The combiner is used to combine intermediate results from parallel execution; each parallel execution starts with the iterator and generates intermediate results. When the parallel execution completes, the separate sets of values are combined with the combiner.</p> <p>You can write analogous code in IDS - using stored procedures or C or Java UDRs.</p> <p>See the SO question <a href="https://stackoverflow.com/questions/715350/show-a-one-to-many-relationship-as-2-columns-1-unique-row-id-comma-separated">Show a one to many relationship as 2 columns — 1 unique row (ID & comma separated list)</a> for a string-based GROUP_CONCAT() function implemented in Informix.</p>

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