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<h1 class="topictitle1">Example: Ensure data integrity with referential constraints</h1>
<div><p>Here is an example of how to ensure data integrity with referential
constraints.</p>
<div class="section"> <p>A database contains an employee file and a department file. Both
files have a department number field named DEPTNO. The related records of
these database files are those for which employee.DEPTNO equals department.DEPTNO.
The desired goal of this example is to ensure that every employee in the employee
file has a corresponding department that they belong to in the department
file. You can accomplish this with a referential constraint.</p>
<ol><li>Use the Add Physical File Constraint (ADDPFCST) command, add a primary
key constraint or a unique constraint to the department file for the DEPTNO
field. This primary key or unique constraint will later become a parent key.
It is not yet a parent key because a referential constraint has not yet been
added.</li>
<li>Add a referential constraint to the employee file using the ADDPFCST command.
The employee file will be the dependent file. The foreign key will be employee.DEPTNO.
The department file will be the parent file with parent key department.DEPTNO.
Because there is either a primary key constraint or a unique constraint with
the DEPTNO field as the key, the constraint will serve as the parent key associated
with the referential constraint.</li>
</ol>
</div>
<div class="section"><p>The referential constraint has update and delete rules that must
be followed for record insert, update, and delete operations on the parent
or the dependent file.</p>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbaforzahfrca.htm" title="These topics discuss how to use referential constraints in your database to ensure that it contains only valid data.">Ensure data integrity with referential constraints</a></div>
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