NULLIF
Syntax
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
.
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
See Also:
-
Appendix C in Oracle Database Globalization Support Guide for the collation determination rules, which define the collation
NULLIF
uses to compare characters fromexpr1
with characters fromexpr2
, and for the collation derivation rules, which define the collation assigned to the return value of this function when it is a character value
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(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 Taylor Whalen AC_ACCOUNT Whalen