IS NULL operator matches the null value.
select empno, ename, comm from emp where comm <= 400 or comm is null;
The IS NULL operator has its own built-in negation option:IS NOT NULL Operator
select ename, job, msal, comm from emp where comm is not null;
IS NULL operator always evaluates to TRUE or FALSE.
SQL> SQL> drop table emp; Table dropped.-- w w w. j av a 2s .c o m SQL> create table emp( 2 empno NUMBER(4) primary key, 3 ename VARCHAR2(8) not null , 4 init VARCHAR2(5) not null , 5 job VARCHAR2(8) , 6 mgr NUMBER(4) , 7 bdate DATE not null , 8 msal NUMBER(6,2) not null , 9 comm NUMBER(6,2) , 10 deptno NUMBER(2) default 10) ; SQL> SQL> insert into emp values(7001,'SMITH','N', 'TRAINER', 7902,date '1975-12-17', 1800 , NULL, 20); SQL> insert into emp values(7002,'ALLEN','JAM','SALESREP',7006,date '1971-05-20', 1600, 300, 30); SQL> insert into emp values(7003,'WARD', 'TF' ,'SALESREP',7006,date '1972-03-02', 1250, 500, 10); SQL> insert into emp values(7004,'JACK', 'JM', 'MANAGER', 7009,date '1977-04-02', 2975, NULL, 20); SQL> insert into emp values(7005,'BROWN','P', 'SALESREP',7006,date '1976-09-28', 1250, 1400, 30); SQL> insert into emp values(7006,'BLAKE','R', 'MANAGER', 7009,date '1973-11-01', 2850, NULL, 10); SQL> insert into emp values(7007,'CLARK','AB', 'MANAGER', 7009,date '1975-06-09', 2450, NULL, 10); SQL> insert into emp values(7008,'SCOTT','DEF','TRAINER', 7004,date '1979-11-26', 3000, NULL, 20); SQL> insert into emp values(7009,'KING', 'CC', 'DIRECTOR',NULL,date '1972-10-17', 5000, NULL, 10); SQL> insert into emp values(7010,'BREAD','JJ', 'SALESREP',7006,date '1978-09-28', 1500, 0, 30); SQL> insert into emp values(7011,'ADAMS','AA', 'TRAINER', 7008,date '1976-12-30', 1100, NULL, 20); SQL> insert into emp values(7012,'JONES','R', 'ADMIN', 7006,date '1979-10-03', 8000, NULL, 30); SQL> insert into emp values(7902,'FORD', 'MG', 'TRAINER', 7004,date '1979-02-13', 3000, NULL, 20); SQL> insert into emp values(7934,'MARY', 'ABC','ADMIN', 7007,date '1972-01-23', 1300, NULL, 10); SQL> SQL> SQL> select empno, ename, comm 2 from emp 3 where comm <= 400 4 or comm is null; EMPNO | ENAME | COMM --------- | -------- | --------- 07001.00 | SMITH | [N/A] 07002.00 | ALLEN | 00300.00 07004.00 | JACK | [N/A] 07006.00 | BLAKE | [N/A] 07007.00 | CLARK | [N/A] 07008.00 | SCOTT | [N/A] 07009.00 | KING | [N/A] 07010.00 | BREAD | 00000.00 07011.00 | ADAMS | [N/A] 07012.00 | JONES | [N/A] 07902.00 | FORD | [N/A] EMPNO | ENAME | COMM --------- | -------- | --------- 07934.00 | MARY | [N/A] 12 rows selected. SQL> SQL> SQL> select ename, job, msal, comm 2 from emp 3 where comm is not null; ENAME | JOB | MSAL | COMM -------- | -------- | --------- | --------- ALLEN | SALESREP | 01600.00 | 00300.00 WARD | SALESREP | 01250.00 | 00500.00 BROWN | SALESREP | 01250.00 | 01400.00 BREAD | SALESREP | 01500.00 | 00000.00 SQL>