105 lines
6.7 KiB
HTML
105 lines
6.7 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.Type" content="concept" />
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<meta name="DC.Title" content="Define the parent file in a referential constraint" />
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<meta name="abstract" content="A parent file must be a physical file with a maximum of one member. You can create a new file or use an existing file when you define the parent file." />
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<meta name="description" content="A parent file must be a physical file with a maximum of one member. You can create a new file or use an existing file when you define the parent file." />
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<meta name="DC.Relation" scheme="URI" content="../cl/addpfcst.htm" />
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<meta name="DC.Relation" scheme="URI" content="../cl/rmvpfcst.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>Define the parent file in a referential constraint</title>
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</head>
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<body id="rbaforzahfrci"><a name="rbaforzahfrci"><!-- --></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">Define the parent file in a referential constraint</h1>
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<div><p>A parent file must be a physical file with a maximum of one member.
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You can create a new file or use an existing file when you define the parent
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file.</p>
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<p>The concept of a parent key applies only in terms of a referential constraint.
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When a referential constraint is added to the dependent file, a parent key
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is required for the parent file. To prepare for this, you must first add either
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a primary key constraint or a unique constraint to the parent file with the
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appropriate set of fields for the key. When the referential constraint is
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added, a search is conducted of unique constraints (and primary key) for a
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match. If a match is found, then the access path of the constraint is used
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as the parent key in the referential constraint relationship.</p>
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<div class="p">To create a new physical file as a parent file, follow these steps:<ol><li>Use the Create Physical File (CRTPF) command to create the file.</li>
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<li>Use the Add Physical File Constraint (ADDPFCST) command to either add
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a primary key constraint or a unique constraint. The primary key can be null-capable,
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but the system creates an implicit check constraint to prevent the insertion
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of null values in the field.</li>
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</ol>
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<div class="note"><span class="notetitle">Note:</span> You can use the SQL CREATE TABLE statement to perform the preceding
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steps with one step.</div>
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</div>
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<p>To use an existing file as a parent file, choose from the following options:</p>
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<ul><li class="liexpand">You can add a primary key constraint to a file with the ADDPFCST command.
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Specify *PRIKEY for the TYPE parameter. You must also specify the key field
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or fields with the KEY parameter. <p>If a primary key constraint already exists
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for the file, the ADDPFCST command with TYPE(*PRIKEY) will fail because a
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file can have only one primary key. If you want a different primary key constraint,
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you must first remove the existing primary key constraint with the Remove
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Physical File Constraint (RMVPFCST) command. Then you can add a new primary
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key constraint.</p>
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</li>
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<li class="liexpand">You can add a unique constraint to a file with the ADDPFCST command. Specify
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*UNQCST for the TYPE parameter. You must also specify the key field or fields
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with the KEY parameter. You can also add a unique constraint with the Structured
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Query Language (SQL) ALTER TABLE statement. <p>If the parent file does not
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have a primary key or unique constraint that can be used as the parent key,
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the system will attempt to automatically add a primary key constraint when
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adding a referential constraint.</p>
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<p>If the parent file has a uniquely keyed
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access path, where the access path fields match the foreign key's fields (both
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for the number of fields and matching attributes), then a primary key constraint
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will be implicitly added to the parent file. This will become the parent key
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for the referential constraint.</p>
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<p>If the parent file is arrival sequence
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access path, then if the fields specified for the parent key match the foreign
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key's fields (matching attributes), then a primary key constraint will be
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implicitly added to the parent file. This will become the parent key for the
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referential constraint.</p>
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</li>
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</ul>
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<div class="section" id="rbaforzahfrci__rbaforzahfrc9"><a name="rbaforzahfrci__rbaforzahfrc9"><!-- --></a><h4 class="sectiontitle">What to do when you cannot define a parent
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key</h4><p>For an existing file with a primary key or unique constraint,
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if neither constraint will suffice as the parent key, there are options you
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can turn to.</p>
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<div class="p">You can take either of the following actions
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when you cannot define a parent key.<ul><li>Delete the file and create it again with the appropriate keys.</li>
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<li>Add a unique or primary key constraint to the created file.</li>
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</ul>
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</div>
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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="rbaforzahfrce.htm" title="You can add referential constraints on physical files with no more than one member. A referential constraint is a file-level attribute; therefore, you can create the constraint before the member exists.">Add referential constraints</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="../cl/crtpf.htm">Create Physical File (CRTPF) command</a></div>
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<div><a href="../cl/addpfcst.htm">Add Physical File Constraint (ADDPFCST) command</a></div>
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<div><a href="../cl/rmvpfcst.htm">Remove Physical File Constraint (RMVPFCST) command</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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