Types of Integrity Constraints

Integrity constraints can be of the following types:

• Check constraints
• Primary key specification
• Candidate key specification
• Referential constraints

An integrity constraint can optionally be referred to by its name. The following example shows the specification of the constraint name, prim_constr, on the supplier_item table:

CREATE TABLE supplier_item (

     supp_no        INTEGER NOT NULL,

     item_no        INTEGER NOT NULL,

     qty            INTEGER NOT NULL DEFAULT 0

     CONSTRAINT prim_constr

     PRIMARY KEY (supp_no, item_no)

) ;

In the above example, note that the constraint name is specified using the keyword, CONSTRAINT.

The following sections give more information on various types of constraints.