Oracle SQL - IS NULL Operator

Introduction

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.

Demo

SQL>
SQL> drop table emp;

Table dropped.-- from  w  w  w. jav  a  2 s  . c om

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>