Example of check constraints - sql, PL-SQL Programming

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Example of Check Constraints

Example: Workaround for when subqueries not permitted in CHECK constraints

CREATE FUNCTION NO_MORE_THAN_20000_ENROLMENTS ( )

RETURNS BOOLEAN;

RETURN (SELECT COUNT (*) FROM IS_ENROLLED_ON) <= 20000;

ALTER TABLE IS_ENROLLED_ON

ADD CONSTRAINT MAX_ENROLMENTS

CHECK (NO_MORE_THAN_20000_ENROLMENTS ( ));

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