80 lines
5.1 KiB
HTML
80 lines
5.1 KiB
HTML
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<?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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<meta name="DC.Title" content="Example: Table function returning document IDs" />
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<meta name="abstract" content="In this example, you have written a table function that returns a row consisting of a single document identifier column for each known document in your text management system that matches a given subject area (the first parameter) and contains the given string (second parameter)." />
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<meta name="description" content="In this example, you have written a table function that returns a row consisting of a single document identifier column for each known document in your text management system that matches a given subject area (the first parameter) and contains the given string (second parameter)." />
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<meta name="DC.subject" content="examples, returning a table function, UDFs (User-defined functions), table function example, CREATE FUNCTION statement" />
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<meta name="keywords" content="examples, returning a table function, UDFs (User-defined functions), table function example, CREATE FUNCTION statement" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Example: Table function returning document IDs</title>
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</head>
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<body id="rbafyudfcfx7"><a name="rbafyudfcfx7"><!-- --></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: Table function returning document IDs</h1>
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<div><p>In this example, you have written a table function that returns
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a row consisting of a single document identifier column for each known document
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in your text management system that matches a given subject area (the first
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parameter) and contains the given string (second parameter).</p>
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<div class="section"><p>This UDF uses the functions of the text management system to quickly
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identify the documents:</p>
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<pre> <strong>CREATE FUNCTION</strong> DOCMATCH (<strong>VARCHAR</strong>(30), <strong>VARCHAR</strong>(255))
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<strong>RETURNS TABLE</strong> (DOC_ID <strong>CHAR</strong>(16))
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<strong>EXTERNAL NAME</strong> 'DOCFUNCS/UDFMATCH(udfmatch)'
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<strong>LANGUAGE C
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PARAMETER STYLE DB2SQL
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NO SQL
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DETERMINISTIC
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NO EXTERNAL ACTION
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NOT FENCED
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SCRATCHPAD
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NO FINAL CALL
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DISALLOW PARALLEL
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CARDINALITY 20</strong></pre>
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<p>Within the context of a single session
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it will always return the same table, and therefore it is defined as DETERMINISTIC.
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The RETURNS clause defines the output from DOCMATCH, including the column
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name DOC_ID. FINAL CALL does not need to be specified for this table function.
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The DISALLOW PARALLEL keyword is required since table functions cannot operate
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in parallel. Although the size of the output from DOCMATCH can be a large
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table, CARDINALITY 20 is a representative value, and is specified to help
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the optimizer make good decisions.</p>
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</div>
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<div class="section"><p>Typically, this table function is used in a join with the table
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containing the document text, as follows:</p>
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<pre> <strong>SELECT</strong> T.AUTHOR, T.DOCTEXT
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<strong>FROM</strong> DOCS <strong>AS</strong> T, <strong>TABLE</strong>(DOCMATCH('MATHEMATICS', 'ZORN''S LEMMA')) <strong>AS</strong> F
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<strong>WHERE</strong> T.DOCID = F.DOC_ID</pre>
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<p>Note the special syntax
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(TABLE keyword) for specifying a table function in a FROM clause. In this
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invocation, the DOCMATCH() table function returns a row containing the single
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column DOC_ID for each MATHEMATICS document referencing ZORN'S LEMMA. These
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DOC_ID values are joined to the master document table, retrieving the author's
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name and document text.</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="rbafyudfdudf.htm" title="A UDF must be registered in the database before the function can be recognized and used by SQL.">Register UDFs</a></div>
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</div>
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</div>
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</body>
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</html>
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