What is a "constraint"

The primary job of a constraint is to enforce a rule in the database. Together, the constraints in a database maintain the integrity of the database. For instance, we have foreign key constraints to ensure all orders reference existing products. You cannot enter an order for a product the database does not know about. Maintaining integrity is of utmost importance for a database, so much so that we cannot trust users and applications to enforce these rules by themselves. Once integrity is lost, you may find customers are double billed, payments to the supplier are missing, and everyone loses faith in your application

http://odetocode.com/articles/79.aspx

http://databases.about.com/od/sqlserver/a/constraints.htm

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Satyapriya Nayak14y ago
The primary job of a constraint is to enforce a rule in the database. Together, the constraints in a database maintain the integrity of the database. For instance, we have foreign key constraints to ensure all orders reference existing products. You cannot enter an order for a product the database does not know about. Maintaining integrity is of utmost importance for a database, so much so that we cannot trust users and applications to enforce these rules by themselves. Once integrity is lost, you may find customers are double billed, payments to the supplier are missing, and everyone loses faith in your application

http://odetocode.com/articles/79.aspx

http://databases.about.com/od/sqlserver/a/constraints.htm

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Vulpes14y ago
Please check this link:

http://msdn.microsoft.com/en-us/library/ms189862(SQL.105).aspx
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