Foreign-key

Constraints on Attributes and Tuples

We have seen key constraints, which compel certain attributes to have distinct values among all the tuples of a relation, and we have seen foreign-key constraints, which enforce referential integrity between attributes of two relations. Now, we shall see a third important kind of

Tuple-Based CHECK Constraints

To declare a constraint on the tuples of a single table R, when we define that table with a CREATE TABLE statement we may add to the list of attributes and key or foreign-key declarations the keyword CHECK followed by a parenthesized condition. This condition can be anything that

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