103 lines
6.4 KiB
HTML
103 lines
6.4 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="Referential integrity and tables" />
|
||
|
|
<meta name="abstract" content="Referential integrity is the condition of a set of tables in a database in which all references from one table to another are valid." />
|
||
|
|
<meta name="description" content="Referential integrity is the condition of a set of tables in a database in which all references from one table to another are valid." />
|
||
|
|
<meta name="DC.subject" content="referential integrity" />
|
||
|
|
<meta name="keywords" content="referential integrity" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafysqlpctablecreate.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafyaddor.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafyaddrcon.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rbafysamptblx.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="rbafyrefinteg" />
|
||
|
|
<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>Referential integrity and tables</title>
|
||
|
|
</head>
|
||
|
|
<body id="rbafyrefinteg"><a name="rbafyrefinteg"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Referential integrity and tables</h1>
|
||
|
|
<div><p>Referential integrity is the condition of a set of tables in a
|
||
|
|
database in which all references from one table to another are valid. </p>
|
||
|
|
<div class="section"><p>Consider
|
||
|
|
the following example: </p>
|
||
|
|
<ul><li>CORPDATA.EMPLOYEE serves as a master list of employees.</li>
|
||
|
|
<li>CORPDATA.DEPARTMENT acts as a master list of all valid department numbers.</li>
|
||
|
|
<li>CORPDATA.EMP_ACT provides a master list of activities performed for projects.</li>
|
||
|
|
</ul>
|
||
|
|
<p>Other tables refer to the same entities described in these tables.
|
||
|
|
When a table contains data for which there is a master list, that data should
|
||
|
|
actually appear in the master list, or the reference is not valid. The table
|
||
|
|
that contains the master list is the <dfn class="term">parent table</dfn>, and the table
|
||
|
|
that refers to it is a <dfn class="term">dependent table</dfn>. When the references from
|
||
|
|
the dependent table to the parent table are valid, the condition of the set
|
||
|
|
of tables is called <dfn class="term">referential integrity</dfn>.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Stated another way, referential integrity is the state of a database
|
||
|
|
in which all values of all foreign keys are valid. Each value of the foreign
|
||
|
|
key must also exist in the parent key or be null. This definition of referential
|
||
|
|
integrity requires an understanding of the following terms: </p>
|
||
|
|
<ul><li>A <dfn class="term">unique key</dfn> is a column or set of columns in a table which
|
||
|
|
uniquely identify a row. Although a table can have several unique keys, no
|
||
|
|
two rows in a table can have the same unique key value.</li>
|
||
|
|
<li>A <dfn class="term">primary key</dfn> is a unique key that does not allow nulls.
|
||
|
|
A table cannot have more than one primary key.</li>
|
||
|
|
<li>A <dfn class="term">parent key</dfn> is either a unique key or a primary key which
|
||
|
|
is referenced in a referential constraint.</li>
|
||
|
|
<li>A <dfn class="term">foreign key</dfn> is a column or set of columns whose values
|
||
|
|
must match those of a parent key. If any column value used to build the foreign
|
||
|
|
key is null, then the rule does not apply.</li>
|
||
|
|
<li>A <dfn class="term">parent table</dfn> is a table that contains the parent key.</li>
|
||
|
|
<li>A <dfn class="term">dependent table</dfn> is the table that contains the foreign
|
||
|
|
key.</li>
|
||
|
|
<li>A <dfn class="term">descendent table</dfn> is a table that is a dependent table or
|
||
|
|
a descendent of a dependent table.</li>
|
||
|
|
</ul>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Enforcement of referential integrity prevents the violation of
|
||
|
|
the rule that states that every non-null foreign key must have
|
||
|
|
a matching parent key.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>SQL supports the referential integrity concept with the CREATE
|
||
|
|
TABLE and ALTER TABLE statements. </p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<ul class="ullinks">
|
||
|
|
<li class="ulchildlink"><strong><a href="rbafyaddor.htm">Add or drop referential constraints</a></strong><br />
|
||
|
|
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.</li>
|
||
|
|
<li class="ulchildlink"><strong><a href="rbafyaddrcon.htm">Add referential constraints</a></strong><br />
|
||
|
|
The rule that every department number shown in the sample employee table must appear in the department table is a referential constraint.</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafysqlpctablecreate.htm" title="A table can be visualized as a two-dimensional arrangement of data consisting of rows and columns.">Create a table</a></div>
|
||
|
|
</div>
|
||
|
|
<div class="relref"><strong>Related reference</strong><br />
|
||
|
|
<div><a href="rbafysamptblx.htm" title="This topic contains the sample tables referred to and used in this topic and the SQL Reference topic collection.">DB2 UDB for iSeries sample 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>
|