Foreign Key

Declaring Foreign-Key Constraints

A second important kind of constraint on a database schema is that values for certain attributes must make sense. That is, an attribute like presC# of relation Studio is expected to refer to a particular movie executive. The implied "referential integrity" constraint is that if a studio's

Maintaining Referential Integrity

We have studied how to declare a foreign key, and we learned that this declaration implies that any set of values for the attributes of the foreign key, none of which are NULL, must also appear in the corresponding attribute(s) of the referenced relation. But how is this constraint

Deferring the Checking of Constraints

Suppose the situation of "Declaring Foreign-Key Constraints" Example 1, where presC# in Studio is a foreign key referencing cert# of MovieExec. Bill Clinton decides, after his national presidency, to found a movie studio, called Redlight Studios, of which he will naturally be the

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