support baseline capturing for `UNION ALL`/`INTERSECT`/`EXCEPT`

[rebelice]

Bug Report

Please answer these questions before submitting your issue. Thanks!

This issue is associated with #19932 and the PR for it doesn't consider baseline capturing.

1. Minimal reproduce step (Required)

drop table if exists t;
create table t(a int, b int, index a(a));
set @@tidb_capture_plan_baselines = on;
select * from t union all select * from t;
select * from t union all select * from t;
show global bindings;

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

Not empty set.

3. What did you see instead (Required)

Empty set.

4. What is your TiDB version? (Required)

MySQL [test]> select tidb_version();
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()

                                                                    |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v4.0.0-beta.2-1559-g6e3d2ecb4
Edition: Community
Git Commit Hash: 6e3d2ecb48a931e835ad4826013e915051c6ebc4
Git Branch: HEAD
UTC Build Time: 2020-11-13 08:38:58
GoVersion: go1.15.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.001 sec)

[rebelice]

/label sig/execution, sig/planner, epic/sql-plan-management

[rebelice]

/assign @rebelice

[rebelice]

/label sig/execution

[rebelice]

The hints of UNION/INTERSECT/EXCEPT will involve a problem. UNION will generate an AGG that is not under any SELECT and INTERSECT/EXCEPT will generate a JOIN that is not under any SELECT. It is not easy to implement on the existing framework, and the changes are large. So it needs design doc and discussion.

[XuHuaiyu]

If we can only reproduce this problem after set @@tidb_capture_plan_baselines = on;, I suppose to change the label from bug to feature-request. @rebelice