expression: wrong results when comparing Decimal and BigInt

[qw4990]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   The reason causing this problem is that when casting a bigint like bigint(11) to decimal, we use the zerofill-length 11 as its type size, so we will do cast(bigint(11) as decimal(11, 0)), which may cause Overflow error.

create table t (
    d decimal(19, 0),
    i bigint(11)
);
insert into t values (123456789012, 123456789012);
select * from t where d = i;

2. What did you expect to see?

mysql> create table t (
    ->     d decimal(19, 0),
    ->     i bigint(11)
    -> );
Query OK, 0 rows affected (0.03 sec)

mysql> 
mysql> insert into t values (123456789012, 123456789012);
Query OK, 1 row affected (0.00 sec)

mysql> select * from t where d = i;
+--------------+--------------+
| d            | i            |
+--------------+--------------+
| 123456789012 | 123456789012 |
+--------------+--------------+
1 row in set (0.00 sec)

3. What did you see instead?

mysql> create table t (
    ->     d decimal(19, 0),
    ->     i bigint(11)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> insert into t values (123456789012, 123456789012);
Query OK, 1 row affected (0.00 sec)

mysql> select * from t where d = i;
Empty set, 1 warning (0.00 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

mysql> select tidb_version();
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                               |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v4.0.0-alpha-309-g181c3a890
Git Commit Hash: 181c3a890df60eee486382cab40415db34d30b2a
Git Branch: master
UTC Build Time: 2019-09-23 03:33:16
GoVersion: go version go1.12 darwin/amd64
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)