Bug #117847 NULLIF Filtering Fails in WHERE Clause

Description:
When using NULLIF in a WHERE clause, MySQL incorrectly includes a row in the result set even though the condition should evaluate to FALSE.

The expected behavior is that if NULLIF(-33.26, ref_1.c1) IS NULL evaluates to FALSE, the row should be filtered out. However, MySQL still returns the row, which seems to be incorrect.

How to repeat:
Create Test Table and Insert Sample Data:
CREATE TABLE `t1` (
  `c1` double
);

INSERT INTO `t1` VALUES (0);

query1:
select  
  ((nullif(-33.26, ref_1.c1)) is null) as w1
from 
  t1 as ref_1;

Result:
+----+
| w1 |
+----+
|  0 |
+----+
1 row in set (0.00 sec)
This correctly shows that NULLIF(-33.26, 0) IS NULL evaluates to FALSE (0).

query2:
select  
  ((nullif(-33.26, ref_1.c1)) is null) as w1
from 
  t1 as ref_1
where ((nullif(-33.26, ref_1.c1)) is null);

Expected Result:
No rows should be returned because the condition evaluates to FALSE.

Actual Result:
+----+
| w1 |
+----+
|  0 |
+----+
1 row in set (0.00 sec)
This result is incorrect because the row should have been filtered out due to the WHERE condition evaluating to FALSE.

mysql version:
github commit: 61a3a1d8ef15512396b4c2af46e922a19bf2b174
version: 9.1.0 

os version:
Linux ubuntu 5.15.0-134-generic #145~20.04.1-Ubuntu SMP Mon Feb 17 13:27:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Hello zhiqiang cheng,

Thank you for the report and test case.

regards,
Umesh