ITPEC FE Morning April 2019 Question 27

Referential Constraint — a constraint defined with FOREIGN KEY and REFERENCES.

A referential constraint ensures that a value in one table must exist as a primary key in another table.

SQL syntax:
FOREIGN KEY (dept_id) REFERENCES Department(id)

Why not others:
- (a) Assertion — a general database-wide condition using CREATE ASSERTION, not tied to foreign keys
- (b) Check constraint — validates column values locally (e.g., CHECK (age > 0)), no cross-table reference
- (c) Key constraint — applies to PRIMARY KEY or UNIQUE, defines uniqueness, not inter-table relationships

Key rule: FOREIGN KEY ... REFERENCES = referential constraint. It enforces referential integrity between two tables.

AI-generated — may contain errors