Cast function should not fail.

[coocood]

select cast("-1" as UNSIGNED) should return 18446744073709551615, but we get "constant -1 overflows bigint" error.

This is because we use Convert function for cast, but actually cast works differently than convert.
cast("xxx" as DATETIME) should returns NULL, but Convert such an invalid time string returns zero time.

[qiuyesuifeng]

select cast("-1" as UNSIGNED) there will get an warning.

mysql> select cast("-1" as UNSIGNED);
+------------------------+
| cast("-1" as UNSIGNED) |
+------------------------+
|   18446744073709551615 |
+------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> show warnings;
+---------+------+-------------------------------------------------------------------------+
| Level   | Code | Message                                                                 |
+---------+------+-------------------------------------------------------------------------+
| Warning | 1105 | Cast to unsigned converted negative integer to it's positive complement |
+---------+------+-------------------------------------------------------------------------+
1 row in set (0.00 sec)

I think we should use error for type cast, like 18446744073709551615 is meaningless and it is difficult to do the same with MySQL.