The result of decimal divide won't round at some precision.

[LittleFall]

Bug Report

1. Minimal reproduce step (Required)

drop table ish;
create table ish(a decimal(4,0), b decimal(40, 20));
alter table ish set tiflash replica 1;
insert into ish values (1, 10001);

set tidb_enforce_mpp=1;
select a/b from ish;

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

+--------+
| a/b    |
+--------+
| 0.0001 |
+--------+

3. What did you see instead (Required)

+--------+
| a/b    |
+--------+
| 0.0000 |
+--------+

4. What is your TiFlash version? (Required)

6.5