69 lines
4.3 KiB
HTML
69 lines
4.3 KiB
HTML
<?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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<head>
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Add or drop referential constraints" />
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<meta name="abstract" content="Constraints are rules that ensure that references from one table, a dependent table, to data in another table, the parent table, are valid. You use referential constraints to ensure referential integrity." />
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<meta name="description" content="Constraints are rules that ensure that references from one table, a dependent table, to data in another table, the parent table, are valid. You use referential constraints to ensure referential integrity." />
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<meta name="DC.subject" content="CREATE TABLE statement, referential constraints, ALTER TABLE statement, constraint, referential, creating tables" />
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<meta name="keywords" content="CREATE TABLE statement, referential constraints, ALTER TABLE statement, constraint, referential, creating tables" />
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<meta name="DC.Relation" scheme="URI" content="rbafyrefinteg.htm" />
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<meta name="DC.Relation" scheme="URI" content="../db2/rbafzmsthctabl.htm" />
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<meta name="DC.Relation" scheme="URI" content="../db2/rbafzmstatabl.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Add or drop referential constraints</title>
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</head>
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<body id="rbafyaddor"><a name="rbafyaddor"><!-- --></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">Add or drop referential constraints</h1>
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<div><p>Constraints are rules that ensure that references from one table,
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a dependent table, to data in another table, the parent table, are valid.
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You use referential constraints to ensure referential integrity.</p>
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<div class="section"><p> Use the SQL CREATE TABLE and ALTER TABLE statements to add or
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change referential constraints.</p>
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</div>
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<div class="section"><p>With a referential constraint, non-null values of the foreign
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key are valid only if they also appear as values of a parent key. When you
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define a referential constraint, you specify: </p>
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<ul><li>A primary or unique key</li>
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<li>A foreign key</li>
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<li>Delete and update rules that specify the action taken with respect to
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dependent rows when the parent row is deleted or updated.</li>
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</ul>
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</div>
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<div class="section"><p>Optionally, you can specify a name for the constraint. If a name
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is not specified, one is automatically generated.</p>
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</div>
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<div class="section"><p>After a referential constraint is defined, the system enforces
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the constraint on every INSERT, DELETE, and UPDATE operation performed through
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SQL or any other interface including iSeries™ Navigator, CL commands, utilities,
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or high-level language statements.</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="rbafyrefinteg.htm" title="Referential integrity is the condition of a set of tables in a database in which all references from one table to another are valid.">Referential integrity and tables</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../db2/rbafzmsthctabl.htm">CREATE TABLE</a></div>
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<div><a href="../db2/rbafzmstatabl.htm">ALTER TABLE</a></div>
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</div>
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</div>
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</body>
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</html> |