Ifnull enum type with not null flag has different result

[wshwsh12]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table if exists t,t2;
create table t(e enum("a","b","c") not null, b int);
create table t2(e enum("a","b","c"), b int);
insert into t values(1,1);
insert into t2 values(1,1);

select * from t where ifnull(e,b);
select * from t2 where ifnull(e,b);

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

Same result.

3. What did you see instead (Required)

[tidb]> select * from t where ifnull(e,b);
+---+------+
| e | b    |
+---+------+
| a |    1 |
+---+------+
1 row in set (0.001 sec)

[tidb]> select * from t2 where ifnull(e,b);
Empty set, 1 warning (0.001 sec)

4. What is your TiDB version? (Required)

master, v5.0,v4.0

[guo-shaoge]

We directly rewrite ifnull to its argument if first argument got not null flag. Check here

[ti-srebot]

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