When the default value is an expression, changing it to a constant by "set default" can be problematic

[zimulala]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table t;
create table t (c int(10), c1 varchar(256)  default rand());
alter table t alter column c1 set default 'xx';
show create table t;
insert into t values (1, default);

drop table t;
create table t (c int(10), c1 varchar(256)  default (REPLACE(UPPER(UUID()), '-', '')));
alter table t alter column c1 set default 'xx';
show create table t;
insert into t values (1, default);

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

mysql> insert into t values (5, default);
Query OK, 1 row affected (0.00 sec)

mysql> insert into t values (5, default);
Query OK, 1 row affected (0.00 sec)

3. What did you see instead (Required)

tidb> show create table t;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                              |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
| t     | CREATE TABLE `t` (
  `c` int(10) DEFAULT NULL,
  `c1` varchar(256) DEFAULT xx
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

tidb> insert into t values (1, default);
ERROR 1054 (42S22): Unknown column 'xx' in 'expression'

4. What is your TiDB version? (Required)

master