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.