73 lines
4.9 KiB
HTML
73 lines
4.9 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<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))' />
|
||
|
|
<meta name="DC.Type" content="reference" />
|
||
|
|
<meta name="DC.Title" content="Table function considerations" />
|
||
|
|
<meta name="abstract" content="An external table function is a UDF that delivers a table to the SQL in which it was referenced. A table function reference is only valid in a FROM clause of a SELECT statement." />
|
||
|
|
<meta name="description" content="An external table function is a UDF that delivers a table to the SQL in which it was referenced. A table function reference is only valid in a FROM clause of a SELECT statement." />
|
||
|
|
<meta name="DC.subject" content="UDFs (User-defined functions), table function, considerations" />
|
||
|
|
<meta name="keywords" content="UDFs (User-defined functions), table function, considerations" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafywudfextern.htm" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="rbafytfconsider" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>Table function considerations</title>
|
||
|
|
</head>
|
||
|
|
<body id="rbafytfconsider"><a name="rbafytfconsider"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Table function considerations</h1>
|
||
|
|
<div><p><span>An external table function is
|
||
|
|
a UDF that delivers a table to the SQL in which it was referenced. A table
|
||
|
|
function reference is only valid in a FROM clause of a SELECT statement.</span></p>
|
||
|
|
<div class="section"><p>When using table functions, observe the following:</p>
|
||
|
|
<ul><li>Even though a table function delivers a table, the physical interface
|
||
|
|
between DB2<sup>®</sup> and
|
||
|
|
the UDF is one-row-at-a-time. There are five types of calls made to a table
|
||
|
|
function: OPEN, FETCH, CLOSE, FIRST, and FINAL. The existence of FIRST and
|
||
|
|
FINAL calls depends on how you define the UDF. The same <em>call-type</em> mechanism
|
||
|
|
that can be used for scalar functions is used to distinguish these calls.</li>
|
||
|
|
<li>The standard interface used between DB2 and user-defined scalar functions is
|
||
|
|
extended to accommodate table functions. The <em>SQL-result</em> argument repeats
|
||
|
|
for table functions; each instance corresponding to a column to be returned
|
||
|
|
as defined in the RETURNS TABLE clause of the CREATE FUNCTION statement. The <em>SQL-result-ind</em> argument
|
||
|
|
likewise repeats, each instance related to the corresponding <em>SQL-result</em> instance.</li>
|
||
|
|
<li>Not every result column defined in the RETURNS clause of the CREATE FUNCTION
|
||
|
|
statement for the table function has to be returned. The DBINFO keyword of
|
||
|
|
CREATE FUNCTION, and corresponding <em>dbinfo</em> argument enable the optimization
|
||
|
|
that only those columns needed for a particular table function reference need
|
||
|
|
be returned.</li>
|
||
|
|
<li>The individual column values returned conform in format to the values
|
||
|
|
returned by scalar functions.</li>
|
||
|
|
<li>The CREATE FUNCTION statement for a table function has a CARDINALITY <em>n</em> specification.
|
||
|
|
This specification enables the definer to inform the DB2 optimizer of the approximate size of
|
||
|
|
the result so that the optimizer can make better decisions when the function
|
||
|
|
is referenced. Regardless of what has been specified as the CARDINALITY of
|
||
|
|
a table function, exercise caution against writing a function with infinite
|
||
|
|
cardinality; that is, a function that always returns a row on a FETCH call. DB2 expects
|
||
|
|
the <em>end-of-table</em> condition, as a catalyst within its query processing.
|
||
|
|
So a table function that never returns the end-of-table condition (SQL-state
|
||
|
|
value '02000') will cause an infinite processing loop.</li>
|
||
|
|
</ul>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafywudfextern.htm" title="You can write the executable code of a UDF in a language other than SQL.">Write UDFs as external functions</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|