update a unsigned column with "-1" result a NULL value when sql_mode=''

[lcwangchao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

> create table t1(a int unsigned);
> set sql_mode='';
> insert into t1 values(0);
> update t1 set a = '-1';
> select a from t1;

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

In MySQL 8.0, it inserts a 0 value:

mysql> select a from t1;
+------+
| a    |
+------+
|    0 |
+------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

In tidb, the updated value is NULL.

TiDB [email protected]:test> select a from t1;
+--------+
| a      |
+--------+
| <null> |
+--------+
1 row in set
Time: 0.009s

4. What is your TiDB version? (Required)

master, but I think it affects all versions