Alter column xx drop default not work in TiDB

[Defined2014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int);
alter table t alter column a drop default;
insert into t values ();

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

mysql> insert into t values ();
ERROR 1364 (HY000): Field 'a' doesn't have a default value

3. What did you see instead (Required)

insert a value NULL

mysql> insert into t values ();
Query OK, 1 row affected (0.01 sec)

4. What is your TiDB version? (Required)

mysql> select tidb_version();
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v6.0.0
Edition: Community
Git Commit Hash: 36a9810441ca0e496cbd22064af274b3be771081
Git Branch: heads/refs/tags/v6.0.0
UTC Build Time: 2022-03-31 10:27:58
GoVersion: go1.18
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)