This Oracle tutorial explains how to use the Oracle/PLSQL NVL function.
The Oracle/PLSQL NVL function can substitute a value for a null value.
NVL() converts a null value to another value.
The format of NVL is:
NVL(x, value)
NVL(x, Avalue) returns Avalue if x is null; otherwise x is returned.
select NVL(null, 'it is a null value') from dual;
The syntax for the Oracle/PLSQL NVL function is:
NVL( string1, replace_with )
string1 is the string to test for a null value.
replace_with is the value returned if string1 is null.
The following SQL statement returns 'n/a' if the city field is a null value. Otherwise, it would return the city value.
SELECT NVL(city, 'n/a')
FROM emp;
This SQL statement returns the name field if the desc contained a null value. Otherwise, it would return the desc.
SELECT id, NVL(desc, name) FROM emp;
The following SQL statement returns 0 if the salary field contained a null value. Otherwise, it would return the salary field.
SELECT NVL(salary, 0) FROM emp;
Mark null value with a descriptive string:
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
JOB VARCHAR2(9),
SAL NUMBER(7, 2),
DEPTNO NUMBER(2));
-- from w ww .j a v a 2 s. c o m
INSERT INTO EMP VALUES (1, null, 'CLERK', 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 empno, NVL(ename, 'Unknown')
2 FROM emp;
EMPNO NVL(ENAME,
---------- ----------
1 Unknown
2 ALLEN
3 WARD
4 JONES
5 MARTIN
6 BLAKE
7 CLARK
8 SCOTT
9 KING
10 TURNER
11 ADAMS
11 rows selected.
SQL>
SQL>