IS NULL, IS NOT NULL
To check if a value is NULL, use the IS NULL operator:
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
HIREDATE DATE);
INSERT INTO EMP VALUES (1, NULL, TO_DATE('17-DEC-1980', 'DD-MON-YYYY'));
INSERT INTO EMP VALUES (2, 'ALLEN', TO_DATE('20-FEB-1981', 'DD-MON-YYYY'));
INSERT INTO EMP VALUES (3, 'WARD', TO_DATE('22-FEB-1981', 'DD-MON-YYYY'));
INSERT INTO EMP VALUES (4, 'JONES', TO_DATE('2-APR-1981', 'DD-MON-YYYY'));
INSERT INTO EMP VALUES (5, 'MARTIN',TO_DATE('28-SEP-1981', 'DD-MON-YYYY'));
SQL> select * from emp where ename is null;
EMPNO ENAME HIREDATE
---------- ---------- ---------
1 17-DEC-80
SQL>
To filter not null value use NOT NULL:
SQL> select * from emp where ename is not null;
EMPNO ENAME HIREDATE
---------- ---------- ---------
2 ALLEN 20-FEB-81
3 WARD 22-FEB-81
4 JONES 02-APR-81
5 MARTIN 28-SEP-81
SQL>