SQL 用cast(num1 as signed)-cast(num2 as signed) 解决报错BIGINT UNSIGNED value is out of range in...

SQL中：两数相减来做查询条件，由于两个字段都是unsigned的，并两个的大小是不一样。所以直接相减查询的时候，会出现负数，导致报错（Mysql不报错）

ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in..

解决方法为：cast(num1 as signed)-cast(num2 as signed)