NOT keyword
You can precede a predicate with the NOT keyword to specify that you want the opposite of the predicate's value (that is, TRUE if the predicate is FALSE).
NOT applies only to the predicate it precedes, not to all predicates in the WHERE clause. For example, to indicate that you are interested in all employees except those working in the department C01, you can say:
... WHERE NOT WORKDEPT = 'C01'which is equivalent to:
... WHERE WORKDEPT <> 'C01'