NULL values
Oracle uses null to represent a unknown value. A null value is not a blank string.
The following example shows that null value is displayed as blank.
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
JOB VARCHAR2(9),
SAL NUMBER(7, 2),
DEPTNO NUMBER(2));
INSERT INTO EMP VALUES (1, NULL, NULL, 800, 20);
INSERT INTO EMP VALUES (2, 'ALLEN', 'SALESMAN', 1600, 30);
INSERT INTO EMP VALUES (3, 'WARD', 'SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (4, 'JONES', 'MANAGER', 2975, 20);
INSERT INTO EMP VALUES (5, 'MARTIN','SALESMAN', 1250, 30);
INSERT INTO EMP VALUES (6, 'BLAKE', 'MANAGER', 2850, 30);
INSERT INTO EMP VALUES (7, 'CLARK', 'MANAGER', 2850, 10);
INSERT INTO EMP VALUES (8, 'SCOTT', 'ANALYST', 3000, 20);
INSERT INTO EMP VALUES (9, 'KING', 'PRESIDENT',3000, 10);
INSERT INTO EMP VALUES (10,'TURNER','SALESMAN', 1500, 30);
INSERT INTO EMP VALUES (11,'ADAMS', 'CLERK', 1500, 20);
SQL> SELECT *
2 FROM emp;
EMPNO ENAME JOB SAL DEPTNO
---------- ---------- --------- ---------- ----------
1 800 20
2 ALLEN SALESMAN 1600 30
3 WARD SALESMAN 1250 30
4 JONES MANAGER 2975 20
5 MARTIN SALESMAN 1250 30
6 BLAKE MANAGER 2850 30
7 CLARK MANAGER 2850 10
8 SCOTT ANALYST 3000 20
9 KING PRESIDENT 3000 10
10 TURNER SALESMAN 1500 30
11 ADAMS CLERK 1500 20
11 rows selected.
SQL>
SQL>
SQL>
SQL>
SQL>