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will not be able to add invalid data or modify valid data so the data becomes invalid, even if the application itself accepts invalid data.

Definition

Each check constraint has to be defined in the CREATE TABLE or ALTER TABLE statement using the syntax:

CREATE TABLE table_name ( ..., CONSTRAINT constraint_name CHECK ( predicate ), ... )

ALTER TABLE table_name ADD CONSTRAINT constraint_name CHECK ( predicate )

If the check constraint refers to a single column only,

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