Incompatible with MySQL when using control functions with bit type

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

use test;
drop table if exists b;
create table b(b bit(8));
insert into b values(97);
select if(1,b,'1') ='a' from b;
select if(1,b,'1') = 97 from b;

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

MySQL [test]> select if(1,b,'1') ='a' from b;
+------------------+
| if(1,b,'1') ='a' |
+------------------+
|                1 |
+------------------+
1 row in set (0.000 sec)

MySQL [test]> select if(1,b,'1') = 97 from b;
+------------------+
| if(1,b,'1') = 97 |
+------------------+
|                1 |
+------------------+
1 row in set (0.000 sec)

3. What did you see instead (Required)

[tidb]> select if(1,b,'1') ='a' from b;
+------------------+
| if(1,b,'1') ='a' |
+------------------+
|                1 |
+------------------+
1 row in set (0.001 sec)

[tidb]> select if(1,b,'1') = 97 from b;
+------------------+
| if(1,b,'1') = 97 |
+------------------+
|                0 |
+------------------+
1 row in set, 1 warning (0.001 sec)

4. What is your TiDB version? (Required)

master

[wzru]

/assign @wzru