"merge" hint in CTE with view will not work

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int);
insert into t values (1);
create view v as select * from t;
explain with cte as (select /+merge()/ * from v) select * from cte;

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

merge in cte works

3. What did you see instead (Required)

mysql> explain with cte as (select * from v) select * from cte;
+--------------------------------+---------+-----------+---------------+--------------------------------+
| id                             | estRows | task      | access object | operator info                  |
+--------------------------------+---------+-----------+---------------+--------------------------------+
| CTEFullScan_11                 | 1.00    | root      | CTE:cte       | data:CTE_0                     |
| CTE_0                          | 1.00    | root      |               | Non-Recursive CTE              |
| └─TableReader_9(Seed Part)     | 1.00    | root      |               | data:TableFullScan_8           |
|   └─TableFullScan_8            | 1.00    | cop[tikv] | table:t       | keep order:false, stats:pseudo |
+--------------------------------+---------+-----------+---------------+--------------------------------+
4 rows in set (0.00 sec)

mysql> explain with cte as (select /*+merge()*/ * from v) select * from cte;
+--------------------------------+---------+-----------+---------------+--------------------------------+
| id                             | estRows | task      | access object | operator info                  |
+--------------------------------+---------+-----------+---------------+--------------------------------+
| CTEFullScan_11                 | 1.00    | root      | CTE:cte       | data:CTE_0                     |
| CTE_0                          | 1.00    | root      |               | Non-Recursive CTE              |
| └─TableReader_9(Seed Part)     | 1.00    | root      |               | data:TableFullScan_8           |
|   └─TableFullScan_8            | 1.00    | cop[tikv] | table:t       | keep order:false, stats:pseudo |
+--------------------------------+---------+-----------+---------------+--------------------------------+
4 rows in set (0.00 sec)

4. What is your TiDB version? (Required)

| Release Version: v6.2.0
Edition: Community
Git Commit Hash: 65f7e2e
Git Branch: heads/refs/tags/v6.2.0
UTC Build Time: 2022-07-27 10:10:50
GoVersion: go1.18.2

[qw4990]

Do we have any document about the hint merge()?

[dayicklp]

Do we have any document about the hint merge()?

doc-cn is merged, and doc will be available soon.