DEPNO	DNAME	LOC
20	RESEARCH	DALLAS
30	SALES	NEW
40	MARKETING	BOSTON
-	UNIQUE Key Constraint (no row may duplicate a value in the constraint's column)	-

DEPNO	DNAME	LOC	Comments
50	SALES	NEW YORK	This row violates the UNIQUE key constraint, because "SALES" is already present in another row; therefore, it is not allowed in the table.
60	N/A	BOSTON	This row is allowed because a null value is entered for the DNAME column; however, if a NOT NULL constraint is alos defined on the DNAME column, this row is not allowed.