Oracle® Database SQL Reference 10g Release 2 (10.2) Part Number B14200-01 |
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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 datatypes, then Oracle Database determines the argument with the higher numeric precedence, implicitly converts the other argument to that datatype, and returns that datatype. If the arguments are not numeric, then they must be of the same datatype, or Oracle returns an error.
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