planner: can't push down predicates with generated columns down through UnionScan

[qw4990]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> create table t (
         id int,
         `deleted_at` datetime(3) NOT NULL DEFAULT '1970-01-01 01:00:01.000',
         `is_deleted` tinyint(1) GENERATED ALWAYS AS ((`deleted_at` > _utf8mb4'1970-01-01 01:00:01.000')) VIRTUAL NOT NULL,
         key k(id, is_deleted)
     );
Query OK, 0 rows affected (0.02 sec)

mysql> 
mysql> begin;
Query OK, 0 rows affected (0.01 sec)

mysql> insert into t (id, deleted_at) values (1, now());
Query OK, 1 row affected (0.00 sec)

mysql> explain select 1 from t where id=1 and is_deleted=true;
+------------------------------+----------+-----------+----------------------------------+--------------------------------------------+
| id                           | estRows  | task      | access object                    | operator info                              |
+------------------------------+----------+-----------+----------------------------------+--------------------------------------------+
| Projection_5                 | 8000.00  | root      |                                  | 1->Column#5                                |
| └─Selection_6                | 8000.00  | root      |                                  | eq(test.t.id, 1), eq(test.t.is_deleted, 1) |
|   └─UnionScan_7              | 10000.00 | root      |                                  |                                            |
|     └─IndexReader_12         | 10000.00 | root      |                                  | index:IndexFullScan_11                     |
|       └─IndexFullScan_11     | 10000.00 | cop[tikv] | table:t, index:k(id, is_deleted) | keep order:false, stats:pseudo             |
+------------------------------+----------+-----------+----------------------------------+--------------------------------------------+
5 rows in set (0.00 sec)

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

The plan should use IndexRangeScan.

3. What did you see instead (Required)

IndexFullScan

4. What is your TiDB version? (Required)

47179ae

[qw4990]

This is caused by this PR #53981, which is to fix a critical bug.

[seiya-annie]

/report customer

[kennedy8312]

/type regression