wrong result when select count/sum(distinct ) from int_col union all decimal_col

[XuHuaiyu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

CREATE TABLE `t` (
  `a` int(11) DEFAULT NULL,
  `b` decimal(6,3) DEFAULT NULL
);

insert into t values(1, 1.000);

2. What did you expect to see?

select count(distinct a) from (select a from t1 union all select b from t1) tmp;

+-------------------+
| count(distinct a) |
+-------------------+
|                 1 |
+-------------------+

3. What did you see instead?

select count(distinct a) from (select a from t1 union all select b from t1) tmp;

+-------------------+
| count(distinct a) |
+-------------------+
|                 2 |
+-------------------+

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

Release Version: v3.0.0-beta-279-g5025d582a
Git Commit Hash: 5025d582a7a69ac9c2f6f8ed744aa23ce687d433
Git Branch: master
UTC Build Time: 2019-03-26 08:35:47
GoVersion: go version go1.12 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false

[XuHuaiyu]

sum also meets this problem

tidb>  select sum(distinct b) from (select b from t union all select a from t) tmp ;

+-----------------+
| sum(distinct b) |
+-----------------+
|           2.000 |
+-----------------+
1 row in set (0.00 sec)