The type of year operation with the type of date is wrong

[mengxin9014]

Bug Report

create table t(a year,b date);
insert into t values(2005,"2004-10-10"),(2015,"2018-03-27");
alter table t set tiflash replica 1;
select * from t where a>b;

1. Minimal reproduce step (Required)

except:

actual:


<!-- a step by step guide for reproducing the bug. -->

### 2. What did you expect to see? (Required)
```mysql
+------+------------+
| a    | b          |
+------+------------+
| 2005 | 2004-10-10 |
+------+------------+

3. What did you see instead (Required)

empty

4. What is your TiDB version? (Required)

v5.0.1

[jebter]

desc select * from t where a>b;
+---------------------+---------+-----------+---------------+--------------------------------------------------+
| id | estRows | task | access object | operator info |
+---------------------+---------+-----------+---------------+--------------------------------------------------+
| TableReader_7 | 1.60 | root | | data:Selection_6 |
| └─Selection_6 | 1.60 | cop[tikv] | | gt(cast(test.t.a, datetime(6) BINARY), test.t.b) |
| └─TableFullScan_5 | 2.00 | cop[tikv] | table:t | keep order:false, stats:pseudo |
+---------------------+---------+-----------+---------------+--------------------------------------------------+

[jebter]

@mengxin9014 This problem has been solved?

[ti-srebot]

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