Description of nullif.gif follows
Description of the illustration nullif.gif


NULLIF compares expr1 and expr2. If they are equal, then the function returns null. If they are not equal, then the function returns expr1. You cannot specify the literal NULL for expr1.

If both arguments are numeric data types, then Oracle Database determines the argument with the higher numeric precedence, implicitly converts the other argument to that data type, and returns that data type. If the arguments are not numeric, then they must be of the same data type, or Oracle returns an error.

The NULLIF function is logically equivalent to the following CASE expression:

CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END


The following example selects those employees from the sample schema hr who have changed jobs since they were hired, as indicated by a job_id in the job_history table different from the current job_id in the employees table:

SELECT e.last_name, NULLIF(j.job_id, e.job_id) "Old Job ID"
  FROM employees e, job_history j
  WHERE e.employee_id = j.employee_id
  ORDER BY last_name, "Old Job ID";

LAST_NAME                 Old Job ID
------------------------- ----------
De Haan                   IT_PROG
Hartstein                 MK_REP
Kaufling                  ST_CLERK
Kochhar                   AC_ACCOUNT
Kochhar                   AC_MGR
Raphaely                  ST_CLERK
Taylor                    SA_MAN
Whalen                    AC_ACCOUNT