The result of query using the tabledual plan is not correct

[lilinghai]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t( a enum('y','b','Abc','null'),b enum('y','b','Abc','null'),key(a));
insert into t values("Abc","Abc");
select * from t where a like "A%";  -- expect got Abc, Abc; but got Empty set
/*
+-------------+---------+------+---------------+---------------+
| id          | estRows | task | access object | operator info |
+-------------+---------+------+---------------+---------------+
| TableDual_5 | 0.00    | root |               | rows:0        |
+-------------+---------+------+---------------+---------------+
*/
select * from t where b like "A%"; -- correctly
/*
+-------------------------+---------+-----------+---------------+--------------------------------+
| id                      | estRows | task      | access object | operator info                  |
+-------------------------+---------+-----------+---------------+--------------------------------+
| TableReader_7           | 0.00    | root      |               | data:Selection_6               |
| └─Selection_6           | 0.00    | cop[tikv] |               | like(rs.t.b, "A%", 92)         |
|   └─TableFullScan_5     | 1.00    | cop[tikv] | table:t       | keep order:false, stats:pseudo |
+-------------------------+---------+-----------+---------------+--------------------------------+
*/

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

tabledual plan result is correct

3. What did you see instead (Required)

tabledual plan result is not correct

4. What is your TiDB version? (Required)

Release Version: v5.2.0-alpha-549-g6720fcd40
Edition: Community
Git Commit Hash: 6720fcd
Git Branch: master
UTC Build Time: 2021-08-09 03:22:37
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

[ti-srebot]

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