143 lines
8.2 KiB
HTML
143 lines
8.2 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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<meta name="DC.Title" content="Example 1: Dynamically join database files without DDS" />
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<meta name="abstract" content="This example shows how to dynamically join database files without DDS." />
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<meta name="description" content="This example shows how to dynamically join database files without DDS." />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Example 1: Dynamically join database files without DDS</title>
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</head>
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<body id="rbafodynjfex1"><a name="rbafodynjfex1"><!-- --></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 1: Dynamically join database files without DDS</h1>
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<div><p>This example shows how to dynamically join database files without
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DDS.</p>
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<div class="section"><p>Assume that you want to join FILEA and FILEB, and the files contain
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the following fields:</p>
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</div>
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<table cellpadding="4" cellspacing="0" border="1" class="tableborder"><tr><td>
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<table cellpadding="4" cellspacing="0" summary="" width="100%" border="0"><thead align="left"><tr><th align="left" valign="bottom" width="33.33333333333333%" id="d0e25">FILEA</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e27">FILEB</th>
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<th align="left" valign="bottom" width="33.33333333333333%" id="d0e29">JOINAB</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e25 ">Cust</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e27 ">Cust</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e29 ">Cust</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e25 ">Name</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e27 ">Amt</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e29 ">Name</td>
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</tr>
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<tr><td align="left" valign="top" width="33.33333333333333%" headers="d0e25 ">Addr</td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e27 "> </td>
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<td align="left" valign="top" width="33.33333333333333%" headers="d0e29 ">Amt</td>
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</tr>
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</tbody>
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</table>
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</td></tr></table>
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<div class="section"><p>The join field is <em>Cust</em> which exists in both files. Any
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record format name can be specified on the Open Query File (OPNQRYF) command
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for the join file. The file does not need a member. The records are not required
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to be in keyed sequence.</p>
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</div>
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<div class="section"><div class="p">You can specify: <pre>OVRDBF FILE(JOINAB) TOFILE(FILEA) SHARE(*YES)
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OPNQRYF FILE(FILEA FILEB) FORMAT(JOINAB) +
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JFLD((FILEA/CUST FILEB/CUST)) +
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MAPFLD((CUST 'FILEA/CUST'))
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CALL PGM(PGME) /* Created using file JOINAB as input */
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CLOF OPNID(FILEA)
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DLTOVR FILE(JOINAB)</pre>
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</div>
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</div>
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<div class="section"><p>File JOINAB is a physical file with no data. This file contains
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the record format to be specified on the FORMAT parameter of the OPNQRYF command.</p>
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</div>
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<div class="section"><p>Notice that the TOFILE parameter on the Override with Database
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File (OVRDBF) command specifies the name of the primary file for the join
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operation (the first file specified for the FILE parameter on the OPNQRYF
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command). In this example, the FILE parameter on the OPNQRYF command identifies
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the files in the sequence they are to be joined (A to B). The format for the
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file is in the file JOINAB.</p>
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</div>
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<div class="section"><div class="p">The JFLD parameter identifies the <em>Cust</em> field in FILEA to
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join to the <em>Cust</em> field in FILEB. Because the <em>Cust</em> field is not
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unique across all of the joined record formats, it must be qualified on the
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JFLD parameter. The system attempts to determine, in some cases, the most
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efficient values even if you do not specify the JFLD parameter on the OPNQRYF
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command. For example, using the previous example, if you specified: <pre>OPNQRYF FILE(FILEA FILEB) FORMAT(JOINAB) +
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QRYSLT('FILEA/CUST *EQ FILEB/CUST') +
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MAPFLD((CUST 'FILEA/CUST'))</pre>
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</div>
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</div>
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<div class="section"><p>The system joins FILEA and FILEB using the <em>Cust</em> field because
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of the values specified for the QRYSLT parameter. Notice that in this example
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the JFLD parameter is not specified on the command. However, if either JDFTVAL(*ONLYDFT)
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or JDFTVAL(*YES) is specified on the OPNQRYF command, the JFLD parameter must
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be specified.</p>
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</div>
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<div class="section"><div class="p">The MAPFLD parameter is needed on the
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Open Query File (OPNQRYF) command to describe which file should be used for
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the data for the <em>Cust</em> field in the record format for file JOINAB. If
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a field is defined on the MAPFLD parameter, its unqualified name (the <em>Cust</em> field
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in this case without the file name identification) can be used anywhere else
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in the OPNQRYF command. Because the <em>Cust</em> field is defined on the MAPFLD
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parameter, the first value of the JFLD parameter need not be qualified. For
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example, the same result can be achieved by specifying: <pre>JFLD((CUST FILEB/CUST)) +
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MAPFLD((CUST 'FILEA/CUST'))</pre>
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</div>
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</div>
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<div class="section"><p>Any other uses of the same field name in the OPNQRYF command to
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indicate a field from a file other than the file defined by the MAPFLD parameter
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must be qualified with a file name.</p>
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</div>
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<div class="section"><p>Because no KEYFLD parameter is specified, the records appear in
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any sequence depending on how the OPNQRYF command selects the records. You
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can force the system to arrange the records the same as the primary file.
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To do this, specify *FILE on the KEYFLD parameter. You can specify this even
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if the primary file is in arrival sequence.</p>
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</div>
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<div class="section"><p>The JDFTVAL parameter (similar to the JDFTVAL keyword in DDS)
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can also be specified on the OPNQRYF command to describe what the system should
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do if one of the records is missing from the secondary file. In this example,
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the JDFTVAL parameter was not specified, so only the records that exist in
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both files are selected.</p>
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</div>
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<div class="section"><p>If you tell the system to improve the results of the query (through
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parameters on the OPNQRYF command), it generally tries to use the file with
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the smallest number of records selected as the primary file. However, the
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system also tries to avoid building a temporary file.</p>
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</div>
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<div class="section"><p>You can force the system to follow the file sequence of the join
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as you have specified it in the FILE parameter on the OPNQRYF command by
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specifying JORDER(*FILE). If JDFTVAL(*YES) or JDFTVAL(*ONLYDFT) is specified,
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the system will never change the join file sequence because a different sequence
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can cause different results.</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="rbafodynjf.htm" title="The dynamic join function allows you to join files without having to first specify data description specifications (DDS) and create a join logical file.">Dynamically join database files without DDS</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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