Bug #100489 negative operands with % yields -0 to be displayed

• Submitted: 11 Aug 2020 4:17
• Modified: 11 Aug 2020 5:42
• Reporter: Yushan ZHANG
• Status: Verified
• Category: MySQL Server: Optimizer
• Severity: S3 (Non-critical)
• Version: 5.7.31, 5.6.48, 8.0.21
• OS: Any
• CPU Architecture: Any

[11 Aug 2020 4:17] Yushan ZHANG

Description:
mysql> select -1 % -1;
+---------+
| -1 % -1 |
+---------+
|       0 |
+---------+
1 row in set (0.01 sec)

-- incorrect, displays `-0`
mysql> SELECT price, price % price FROM t1;
+-------+---------------+
| price | price % price |
+-------+---------------+
|    -1 |            -0 |
+-------+---------------+
1 row in set (0.00 sec)

How to repeat:
select -1 % -1;

drop table if exists t1;

create table t1(
price float
);

insert into t1 values (-1);

SELECT price, price % price FROM t1;

Suggested fix:
fix the result when evaluating an expression with the field

[11 Aug 2020 5:42] MySQL Verification Team

Hello Yushan ZHANG,

Thank you for the report and test case.
Observed that 5.6.48, 5.7.31 and 8.0.21 are affected.

regards,
Umesh