Incompatible with MySQL when using expressions returning enum as WHERE conditions

[dyzsr]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists e;
create table e(e enum('c', 'b', 'a'));
insert into e values ('a'),('b'),('a'),('b');
select e from e where if(e>1, e, e);
select e from e where case e when 1 then e else e end;

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

MySQL 8.0.22

mysql root@localhost:test> select e from e where if(e>1, e, e);
+---+
| e |
+---+
| a |
| b |
| a |
| b |
+---+
4 rows in set
Time: 0.007s

mysql root@localhost:test> select e from e where case e when 1 then e else e end;
+---+
| e |
+---+
| a |
| b |
| a |
| b |
+---+
4 rows in set
Time: 0.013s

mysql root@localhost:test> select if(e>1,e,e)='a' from e
+-----------------+
| if(e>1,e,e)='a' |
+-----------------+
| 1               |
| 0               |
| 0               |
+-----------------+
3 rows in set
Time: 0.060s

mysql root@localhost:test> select if(e>1,e,e)=1 from e
+---------------+
| if(e>1,e,e)=1 |
+---------------+
| 0             |
| 0             |
| 1             |
+---------------+
3 rows in set
Time: 0.008s

3. What did you see instead (Required)

mysql root@127.0.0.1:test> select e from e where if(e>1, e, e);
+---+
| e |
+---+
0 rows in set
Time: 0.009s

mysql root@127.0.0.1:test> select e from e where case e when 1 then e else e end;
+---+
| e |
+---+
0 rows in set
Time: 0.011s

mysql root@127.0.0.1:test> select if(e>1,e,e)='a' from e;
+-----------------+
| if(e>1,e,e)='a' |
+-----------------+
| 1               |
| 0               |
| 0               |
+-----------------+
3 rows in set
Time: 3.559s

mysql root@127.0.0.1:test> select if(e>1,e,e)=1 from e;
+---------------+
| if(e>1,e,e)=1 |
+---------------+
| 0             |
| 0             |
| 0             |
+---------------+
3 rows in set
Time: 0.014s

4. What is your TiDB version? (Required)

tidb_version() | Release Version: v4.0.0-beta.2-2275-g5f73c822c
Edition: Community
Git Commit Hash: 5f73c822cabbf5dab31f37fa17437c2b041fd516
Git Branch: master
UTC Build Time: 2021-03-04 09:55:51
GoVersion: go1.15
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

5. Root cause analysis

The eval type of if(e>1, e, e) is evaluated as ETString. Enum value 'a' as string becomes 0 when converting to int.

Maybe we should consider adding Enum/Set as separate eval types.
Related RFC: https://github.com/tikv/rfcs/pull/57/files

[dyzsr]

/sig execution
/component expression

[guo-shaoge]

drop table t1;
create table t1(c1 enum('a', 'b'));
insert into t1 values('a');
select if(c1 > -1, c1, 1) > 1 from t1;

mysql> select (case when c1 then c1 end) > 1 from t1;
ERROR 1105 (HY000): baseBuiltinFunc.evalInt() should never be called, please contact the TiDB team for help

Same reason here: Expression don't return enum/set type when deduce type.

CaseWhen expr's eval function is builtinCaseWhenStringSig, which only implement EvalString, but GT expr need EvalInt().

[ti-srebot]

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