ALTER TABLE t CHANGE a b (rename column) does not work for generated columns

[mjonss]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t (a int, b int as (a+3));
alter table t change a c int not null;

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

Success (propagate the rename into the generated column expression) or this MySQL compatible error:

mysql> create table t (a int, b int as (a+3));
Query OK, 0 rows affected (0,03 sec)

mysql> alter table t change a c int not null;
ERROR 3108 (HY000): Column 'a' has a generated column dependency.

3. What did you see instead (Required)

tidb> create table t (a int, b int as (a+3));
Query OK, 0 rows affected (0,08 sec)

tidb> alter table t change a c int not null;
ERROR 1054 (42S22): Unknown column 'a' in 'generated column function'

4. What is your TiDB version? (Required)

tidb_version(): Release Version: v6.5.0-alpha
Edition: Community
Git Commit Hash: 18cb721079e96e973bf1fc56b5583bc75455b4ba
Git Branch: heads/refs/tags/v6.5.0-alpha
UTC Build Time: 2022-11-08 14:32:53
GoVersion: go1.19.2
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: tikv

[mjonss]

Somewhat related to #38932 (i.e. rename of column with dependency of other expression).

[bb7133]

I've checked the behavior of PG & CRDB, they would rewrite the column name in the expression index, thus allowing the rename of the column name.

So I think it's fine to just report the error, or allow the rename like PG & CRDB.