different behavior from mysql planner with a condition caused error.

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

CREATE TABLE ttt (
a int(10) unsigned,
b int(10) unsigned
);
insert into ttt values(1,10),(20,2);
select * from ttt where a-b>0 and a = 1 and b = 9;

2. What did you expect to see? (Required)

In MySQL 8.0

MySQL [test]>  select * from ttt where a-b>0 and a = 1 and b = 9;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(1 - 9)'

3. What did you see instead (Required)

[tidb]> select * from ttt where a-b>0 and a = 1 and b = 9;
Empty set (0.001 sec)
[tidb]> desc select * from ttt where a-b>0 and a = 1 and b = 9;
+-------------+---------+------+---------------+---------------+
| id          | estRows | task | access object | operator info |
+-------------+---------+------+---------------+---------------+
| TableDual_5 | 1.60    | root |               | rows:0        |
+-------------+---------+------+---------------+---------------+
1 row in set (0.001 sec)

4. What is your TiDB version? (Required)

6cd3c65

[wshwsh12]

Of course, it may be a MySQL bug. Because the condition is always false and it should get an empty result.

[zhangysh1995]

Of course, it may be a MySQL bug. Because the condition is always false and it should get an empty result.

@wshwsh12 I think it is probably not a bug in MySQL. You see that a and b are unsigned int, and a-b compute negative numbers in a signed case but it will cause an underflow in an unsigned case, where you will get a super big number as the result. It is reasonable that MySQL returned the out of range error. Therefore, the bug is in TiDB not in MySQL. Basically, the first predicate a-b>0 is always positive and the query should NOT return any result but should raise an error.