wrong join results with enum value.

[SunRunAway]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

create table tenum( col ENUM ('value1','value2','value3'), col2 ENUM('v1', 'v2', 'v3') );
insert into tenum values(1, 1);

2. What did you expect to see?

mysql> select * from tenum t1 inner join tenum t2 on t1.col = t2.col2;
Empty set (0.00 sec)

3. What did you see instead?

mysql> select * from tenum t1 inner join tenum t2 on t1.col = t2.col2;
+--------+------+--------+------+
| col    | col2 | col    | col2 |
+--------+------+--------+------+
| value1 | v1   | value1 | v1   |
+--------+------+--------+------+
1 row in set (0.00 sec)

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

4.0-rc1

[SunRunAway]

Maybe type SET has a similar issue.

[SunRunAway]

Duplicate of #18850