only_full_group_by is checked wrongly

[XuHuaiyu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

mysql> create table t(tp_real real);
mysql> select tp_real from t group by (tp_real);
mysql> select tp_real from t group by tp_real;

2. What did you expect to see?

mysql> create table t(tp_real real);
Query OK, 0 rows affected (0.12 sec)

mysql> select tp_real from t group by (tp_real);
Empty set (0.04 sec)

mysql> select tp_real from t group by tp_real;
Empty set (0.04 sec)

3. What did you see instead?

mysql> create table t(tp_real real);
Query OK, 0 rows affected (0.12 sec)

mysql> select tp_real from t group by (tp_real);
ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'test.t.tp_real' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

mysql> select tp_real from t group by tp_real;
Empty set (0.04 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   mysql> select tidb_Version();
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | tidb_Version() |
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | Release Version: v4.0.0-alpha-822-ge9f19970d
   Git Commit Hash: e9f1997
   Git Branch: master
   UTC Build Time: 2019-11-11 01:44:23
   GoVersion: go version go1.13.1 linux/amd64
   Race Enabled: false
   TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
   Check Table Before Drop: false |
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   1 row in set (0.03 sec)