overflow compability

[winkyao]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

select -9223372036854775809;

2. What did you expect to see?

9223372036854775809 is overflow math.MaxInt64, but mysql convert it to Decimal type.

mysql> select -9223372036854775809;
Field   1:  `-9223372036854775809`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       NEWDECIMAL
Collation:  binary (63)
Length:     20
Max_length: 20
Decimals:   0
Flags:      NOT_NULL BINARY NUM


+----------------------+
| -9223372036854775809 |
+----------------------+
| -9223372036854775809 |
+----------------------+
1 row in set (0.00 sec)

3. What did you see instead?

but TiDB return 9223372036854775807 caused by int overflow, and still use LONGLONG type;

mysql> select -9223372036854775809;
Field   1:  `-9223372036854775809`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       LONGLONG
Collation:  binary (63)
Length:     0
Max_length: 19
Decimals:   31
Flags:      BINARY NUM


+----------------------+
| -9223372036854775809 |
+----------------------+
|  9223372036854775807 |
+----------------------+
1 row in set (0.00 sec)

4. What version of TiDB are you using (tidb-server -V)?

[winkyao]

#3691