wrong result in the combined expression

[ChenPeng2013]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use test;
drop table if exists t;
create table t(a enum("a", "b"), b enum("a", "b"), c bool);
insert into t values("a", "a", 1);
select * from t t1 right join t t2 on t1.a=t2.b;
select * from t t1 right join t t2 on t1.a=t2.c;
select * from t t1 right join t t2 on t1.a=t2.b and t1.a= t2.c;

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

release-5.0 & release-4.0

mysql> select * from t t1 right join t t2 on t1.a=t2.b;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| a    | a    |    1 | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.00 sec)

mysql> select * from t t1 right join t t2 on t1.a=t2.c;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| a    | a    |    1 | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.01 sec)

mysql> select * from t t1 right join t t2 on t1.a=t2.b and t1.a= t2.c;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| a    | a    |    1 | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

release-5.1 & release-5.2 & master

mysql> select * from t t1 right join t t2 on t1.a=t2.b;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| a    | a    |    1 | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.00 sec)

mysql> select * from t t1 right join t t2 on t1.a=t2.c;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| a    | a    |    1 | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.00 sec)

mysql> select * from t t1 right join t t2 on t1.a=t2.b and t1.a= t2.c;
+------+------+------+------+------+------+
| a    | b    | c    | a    | b    | c    |
+------+------+------+------+------+------+
| NULL | NULL | NULL | a    | a    |    1 |
+------+------+------+------+------+------+
1 row in set (0.00 sec)

4. What is your TiDB version? (Required)

[wshwsh12]

In this case, t1.a should use ETString in t1.a=t2.b and use ETInt in t1.a=t2.c. We use the flag to distinguish them.
When building hashJoin, the flag have been overwritten by mistake, because t1.a use the same column index for the two conditions.

tidb/executor/builder.go

Lines 1260 to 1265 in efec5c3

	for _, key := range e.buildKeys {
	e.buildTypes[key.Index].Flag = key.RetType.Flag
	}
	for _, key := range e.probeKeys {
	e.probeTypes[key.Index].Flag = key.RetType.Flag
	}

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.