union result is not differ from mysql

[XuHuaiyu]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

create table t(a int);
create table s(a int unsigned);

insert into t value(-1);
insert into s value(1);

2. What did you expect to see?

select * from t union all select * from s;
+------+
| a    |
+------+
|   -1 |
|    1 |
+------+

select * from s union all select * from t;
+------+
| a    |
+------+
|    0 |
|    1 |
+------+

3. What did you see instead?

select * from t union all select * from s;
+------+
| a    |
+------+
|   -1 |
|    1 |
+------+

select * from s union all select * from t;
+------+
| a    |
+------+
|   -1 |
|    1 |
+------+

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

Release Version: v2.1.0-beta-61-g44e34bd-dirty
Git Commit Hash: 44e34bd30468fb35df4526d37c8511b259c6794d
Git Branch: castintasdecimal
UTC Build Time: 2018-07-17 09:39:23
GoVersion: go version go1.10.1 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e

[zz-jason]

The result of mysql seems strange... Is it mysql 5.7?

[XuHuaiyu]

yes, mysql 5.7
I think it's somewhat reasonable,
since the result type is an aggregate type of two types.

And it seems the unsigned flag of the first column
would affect the final type unsigned flag.