Check constraint: Difference between revisions

Revision as of 12:26, 17 December 2005

Revision as of 12:32, 17 December 2005

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A check constraint is a rule that defines valid [[data]] when adding or updating an entry in a [[database]]. A check constraint is applied to a column in the database. The constraint must be a [[Boolean expression]].

For example, in a database containing products, you could add a check constraint such that the price of a product and quantity of a product is either zero or a positive value:

PRICE >= 0

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If these constraints are not in place, it would be possible to have a negative price (-$30) or quantity (-3 items).

Check constraints are used to ensure the validity of data in a database i.e. provide [[data integrity]]. If they are used at the database level, applications which use the database will not be able to add invalid data or modify invalidvalid data toso theit databasebecomes invalid, even if the application itself accpets invalid data.