cast datetime as decimal wrong result

[guo-shaoge]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table test.t1;
create table test.t1(c1 datetime(5));
insert into test.t1 values('2022-10-10 10:10:10.12345');
alter table test.t1 set tiflash replica 1;
set @@tidb_isolation_read_engines='tiflash'; set @@tidb_enforce_mpp = 1; select cast(test.t1.c1 as decimal(17, 3)) from test.t1;

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

mysql> select cast(test.t1.c1 as decimal(17, 3)) from test.t1;
+------------------------------------+
| cast(test.t1.c1 as decimal(17, 3)) |
+------------------------------------+
|                 20221010101010.123 |
+------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

mysql> select cast(test.t1.c1 as decimal(17, 3)) from test.t1;
+------------------------------------+
| cast(test.t1.c1 as decimal(17, 3)) |
+------------------------------------+
|                  1774256937300.572 |
+------------------------------------+
1 row in set (0.01 sec)

4. What is your TiFlash version? (Required)

master