The result of TiDB's expression CastRealAsTime() is inconsistent with Mysql.

[mengxin9014]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

 create table test (d1 double, d2 decimal(10,2));
 insert into test values(111.1, 111.1);
 select cast(d1 as datetime), cast(d2 as datetime) from test;

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

+----------------------+----------------------+
| cast(d1 as datetime) | cast(d2 as datetime) |
+----------------------+----------------------+
| 2000-01-11 00:00:00  | 2000-01-11 00:00:00  |
+----------------------+----------------------+

3. What did you see instead (Required)

+----------------------+----------------------+
| cast(d1 as datetime) | cast(d2 as datetime) |
+----------------------+----------------------+
| NULL                 | 2000-01-11 00:00:00  |
+----------------------+----------------------+

4. What is your TiDB version? (Required)

nightly