Missing decimal M and D check

[blacktear23]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

mysql> create table td(d decimal(10, 5));
Query OK, 0 rows affected (0.01 sec)

mysql> select * from td where d = cast(0 as decimal(10,20));
Empty set (0.00 sec)

mysql> select * from td where d = cast(0 as decimal(1000,20));
Empty set (0.00 sec)

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

mysql> create table td(d decimal(10, 5));
Query OK, 0 rows affected (0.01 sec)

mysql> select * from td where d = cast(0 as decimal(10,20));
ERROR 1427 (42000): For float(M,D), double(M,D) or decimal(M,D), M must be >= D (column '').

mysql> select * from td where d = cast(0 as decimal(1000,20));
ERROR 1426 (42000): Too big precision 1000 specified for column '0'. Maximum is 65.
mysql>

3. What did you see instead (Required)

mysql> create table td(d decimal(10, 5));
Query OK, 0 rows affected (0.01 sec)

mysql> select * from td where d = cast(0 as decimal(10,20));
Empty set (0.00 sec)

mysql> select * from td where d = cast(0 as decimal(1000,20));
Empty set (0.00 sec)

4. What is your TiDB version? (Required)

tidb_version(): Release Version: v4.0.0-beta.2-1568-ga35e3fd5c-dirty
Edition: Community
Git Commit Hash: a35e3fd5c7b3a7be73d35a7314e1eb6542950715
Git Branch: refactor-parser-config-update
UTC Build Time: 2020-11-13 12:41:20
GoVersion: go1.15.2
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.00 sec)

[wjhuang2016]

Closed by #21845

[ti-srebot]

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