What is a constraint

Question

Hi friends What is a constraint?

Satyapriya Nayak · Answer

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

Vulpes · Answer

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

What is a "constraint"