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The Query Optimizer can use constraints to help it select the best performing query. In order to get the best performance, it is important that you use them appropriately throughout your database application, such as using them for primary keys, unique keys, primary keys, and so on. [6.5, 7.0, 2000, 2005] Updated 11-6-2006
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If you have a choice between using a trigger or a CHECK constraint to enforce rules or defaults within your SQL Server databases, you will generally want to choose a CHECK constraint, as they are faster than using triggers when performing the same task. [6.5, 7.0, 2000, 2005] Updated 11-6-2006
