Using the FOREIGN KEY Constraint

A foreign key joins and establishes dependencies between tables. That is, it creates a referential constraint. (For more information on referential constraints, see the REFERENCES Clause.)

A foreign key references a unique or primary key in a table. For every entry in the foreign-key columns, a matching entry must exist in the unique or primary-key columns if all foreign-key columns contain non-NULL values.

You cannot specify BYTE or TEXT columns as foreign keys.

You cannot specify BLOB or CLOB columns as foreign keys.


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