Different result from MySQL using DIV with decimal type.

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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.

create table test1(a decimal(10,4) unsigned, b float);
insert into test1 value(1.0090, -1);
SELECT   ( `a` DIV  `b`  )   FROM test1;

2. What did you expect to see?

In MySQL,

mysql> SELECT   ( `a` DIV  `b`  )   FROM test1;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(`randgen_test`.`test1`.`a` DIV `randgen_test`.`test1`.`b`)'

3. What did you see instead?

In TiDB,

mysql> SELECT   ( `a` DIV  `b`  )   FROM test1;
+----------------------+
| ( `a` DIV  `b`  )    |
+----------------------+
| 18446744073709551615 |
+----------------------+
1 row in set (0.00 sec)

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   fdbc149