Syntax
nullif::=
Text description of nullif
Purpose
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.
The NULLIF function is logically equivalent to the following CASE expression:
CASE WHEN expr1 = expr 2 THEN NULL ELSE expr1 END
Examples
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(e.job_id, j.job_id) "Old Job ID"
FROM employees e, job_history j
WHERE e.employee_id = j.employee_id
ORDER BY last_name;
LAST_NAME Old Job ID
------------------------- ----------
De Haan AD_VP
Hartstein MK_MAN
Kaufling ST_MAN
Kochhar AD_VP
Kochhar AD_VP
Raphaely PU_MAN
Taylor SA_REP
Taylor
Whalen AD_ASST
Whalen
