47 lines
3.0 KiB
HTML
47 lines
3.0 KiB
HTML
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<meta name="DC.Title" content="Primary key constraints" />
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<meta name="abstract" content="A primary key constraint is a unique key with special attributes that make the key the primary access path for the file." />
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<title>Primary key constraints</title>
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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">Primary key constraints</h1>
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<div><p>A primary key constraint is a unique key with special attributes
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that make the key the primary access path for the file.</p>
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<p>Primary key constraints identify a field or set of fields
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in a database file whose values must be unique across records in the file.
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The field must be in ascending order, and can be null-capable. If it is null-capable,
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a check constraint is implicitly added so that null values cannot be entered
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in the field. You can define only one primary key constraint for a file.</p>
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<p>A primary key constraint can be used as the parent key when adding a referential
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constraint.</p>
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbaforzahfcoa.htm" title="A constraint is a restriction or limitation placed on a file to ensure that the data in your database remains consistent as you add, change, and remove records. These topics describe how to use constraints to ensure data consistency.">Control the integrity of your database with constraints</a></div>
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