incompatible behavior for aggregation in subquery with MySQL

[eurekaka]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

In TiDB:

mysql> create table tbl(a int, b int);
Query OK, 0 rows affected (0.01 sec)

mysql> select t1.a, t1.b, (select max(t2.b) from tbl t2 where t2.a in (select t3.b from tbl t3 where t3.a = t1.a)) as agg_col
    -> from tbl t1 WHERE t1.b = 2;
ERROR 1140 (42000): In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column 'a'; this is incompatible with sql_mode=only_full_group_by

mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode                                                                                                                                |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+

2. What did you expect to see?

In MySQL:

mysql> select t1.a, t1.b, (select max(t2.b) from tbl t2 where t2.a in (select t3.b from tbl t3 where t3.a = t1.a)) as agg_col
    -> from tbl t1 WHERE t1.b = 2;
Empty set (0.00 sec)

mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode                                                                                                                                |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+

3. What did you see instead?

TiDB has inconsistent behavior with MySQL.

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

Git Commit Hash: 4f232e5c8d3f65c5b21c71761613c06e1bc2538a
Git Branch: master
UTC Build Time: 2019-03-01 06:04:07
GoVersion: go version go1.11.1 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false