Following up on yesterday's post from Louis, sometimes you encounter databases with missing referential integrity constraints. Even when the database is intended to have RI, accidents happen. Maybe a script dropped RI constraints before a bulk load and didn't quite get all of the constraints recreated. Whatever the reason, it's good to have a script to identify tables that are not referenced and do not reference other tables. Here's a script that works on SQL Server 2005 and 2008 (updated to no longer use sysreferences as per Adam Machanic's suggestion):
LEFT JOIN sys.foreign_keys referenced
ON sys.objects.object_id = referenced.referenced_object_id
LEFT JOIN sys.foreign_keys parent
ON sys.objects.object_id = parent.parent_object_id
WHERE sys.objects.type = 'U'
AND referenced.referenced_object_id IS NULL
AND parent.parent_object_id IS NULL
Louis did a good job explaining the importance of using the database engine to protect the integrity of the data. As a consultant, I've seen lots of databases with varying degrees of referential integrity. It never works out well in the long run when referential integrity isn't enforced in the database. Application code - even if it is christened object relational mapping - is no substitute for imposing referential integrity checks in the database. A relational database is more than a data storage repository - and it should be.
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About John Paul Cook
John Paul Cook is both a Registered Nurse and a Microsoft SQL Server MVP experienced in Microsoft SQL Server and Oracle database application design, development, and implementation. He has spoken at many conferences including Microsoft TechEd and the SQL PASS Summit. He has worked in oil and gas, financial, manufacturing, and healthcare industries. Experienced in systems integration and workflow analysis, John is passionate about combining his IT experience with his nursing background to solve difficult problems in healthcare. He sees opportunities in using business intelligence to satisfy healthcare meaningful use requirements and improve patient outcomes. Contributing author to SQL Server MVP Deep Dives
and SQL Server MVP Deep Dives Volume 2