alter table failed with bit column

[tohghua]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   create table t (i int, b bit);
   alter table t modify b bit first;

2. What did you expect to see?
   sql runs successfully.

3. What did you see instead?
   SQL Error [1105] [HY000]: unsupported modify column unsigned false not match origin true

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   Release Version: v2.1.16
   Git Commit Hash: 86ad1a9
   Git Branch: HEAD
   UTC Build Time: 2019-08-15 10:21:49
   GoVersion: go version go1.12 linux/amd64
   Race Enabled: false
   TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
   Check Table Before Drop: false

[zz-jason]

@zimulala PTAL

[zimulala]

@tohghua
Thanks for your feedback!
I will fix it.

[tohghua]

@zimulala
Thanks!
This sql also fails:
create table t (i int, b bit);
alter table t modify b int;
alter table t modify b int unsigned;

[tohghua]

@zimulala Execuse me, how is it going now?

[zimulala]

@tohghua

create table t (i int, b bit);
alter table t modify b int;
alter table t modify b int unsigned;

We don't support these DDLs. For support on the "modify/change column" operation, you can refer to the docs.