planner: full-group checking cannot handle case sensitivity correctly

[qw4990]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t (a varchar(12));
select substr(a, 12, 1) from t group by SUBSTR(a, 12, 1);

2. What did you expect to see? (Required)

The query can be processed without any error.

3. What did you see instead (Required)

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

4. What is your TiDB version? (Required)

mysql> select tidb_version();
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                            |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v5.2.0-alpha-793-gda7b00124
Edition: Community
Git Commit Hash: da7b00124b35dbe5cdb044224209857498879df5
Git Branch: master
UTC Build Time: 2021-09-01 07:19:56
GoVersion: go1.16.3
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

[zhangjinpeng87]

Have we located the root cause?

[time-and-fate]

Have we located the root cause?

It's because ExpressionDeepEqual doesn't implement comparing ExprNodes case-insensitively.

[AilinKid]

winoros#7 In our latest feature branch, this case has been resolved.