| 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) |
| 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 | 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. |