precision problems when handling decimal calculation

[qw4990]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

mysql root@127.0.0.1:test> create table t (a int);                                                                                        
mysql root@127.0.0.1:test> insert into t values (42);                                                                                     
mysql root@127.0.0.1:test> select * from t where a / 1000000;                                                                             

2. What did you expect to see?

mysql root@127.0.0.1:test> create table t (a int);                                                                                        
Query OK, 0 rows affected
Time: 0.596s
mysql root@127.0.0.1:test> insert into t values (42);                                                                                     
Query OK, 1 row affected
Time: 0.211s
mysql root@127.0.0.1:test> select * from t where a / 1000000;                                                                             
+----+
| a  |
+----+
| 42 |
+----+
1 row in set
Time: 0.030s

3. What did you see instead?

mysql root@127.0.0.1:test> create table t (a int);                                          
Query OK, 0 rows affected
Time: 0.025s
mysql root@127.0.0.1:test> insert into t values (42);                                       
Query OK, 1 row affected
Time: 0.005s
mysql root@127.0.0.1:test> select * from t where a / 1000000;                               
+---+
| a |
+---+
0 rows in set

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

The latest master branch.