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This form validates a foreign key or check constraint that was previously created as
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NOT VALID, by scanning the table to ensure there are no rows for which the constraint is not satisfied\&. Nothing happens if the constraint is already marked valid\&. The value of separating validation from initial creation of the constraint is that validation requires a lesser lock on the table than constraint creation does\&.
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lock\&. The value of separating validation from initial creation is that you can defer validation to less busy times, or can be used to give additional time to correct pre\-existing errors while preventing new errors\&.
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DROP CONSTRAINT [ IF EXISTS ]