<?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="Add or drop referential constraints" /> <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." /> <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." /> <meta name="DC.subject" content="CREATE TABLE statement, referential constraints, ALTER TABLE statement, constraint, referential, creating tables" /> <meta name="keywords" content="CREATE TABLE statement, referential constraints, ALTER TABLE statement, constraint, referential, creating tables" /> <meta name="DC.Relation" scheme="URI" content="rbafyrefinteg.htm" /> <meta name="DC.Relation" scheme="URI" content="../db2/rbafzmsthctabl.htm" /> <meta name="DC.Relation" scheme="URI" content="../db2/rbafzmstatabl.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="rbafyaddor" /> <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>Add or drop referential constraints</title> </head> <body id="rbafyaddor"><a name="rbafyaddor"><!-- --></a> <!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script> <h1 class="topictitle1">Add or drop referential constraints</h1> <div><p>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.</p> <div class="section"><p> Use the SQL CREATE TABLE and ALTER TABLE statements to add or change referential constraints.</p> </div> <div class="section"><p>With a referential constraint, non-null values of the foreign key are valid only if they also appear as values of a parent key. When you define a referential constraint, you specify: </p> <ul><li>A primary or unique key</li> <li>A foreign key</li> <li>Delete and update rules that specify the action taken with respect to dependent rows when the parent row is deleted or updated.</li> </ul> </div> <div class="section"><p>Optionally, you can specify a name for the constraint. If a name is not specified, one is automatically generated.</p> </div> <div class="section"><p>After a referential constraint is defined, the system enforces the constraint on every INSERT, DELETE, and UPDATE operation performed through SQL or any other interface including iSeries™ Navigator, CL commands, utilities, or high-level language statements.</p> </div> </div> <div> <div class="familylinks"> <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> </div> <div class="relinfo"><strong>Related information</strong><br /> <div><a href="../db2/rbafzmsthctabl.htm">CREATE TABLE</a></div> <div><a href="../db2/rbafzmstatabl.htm">ALTER TABLE</a></div> </div> </div> </body> </html>