百度之后说:
mysql处理两个整数(INT)相减的时候,如果其中有一个是UNSIGNED INT类型的,那么结果就被当做是UNSIGNED的。
阿神2017-04-17 15:31:20
If the result of the subtraction is a negative number, it will be out of range
because your type is an unqualified integer, such as greater than or equal to 0. All versions of this should be the same, it’s a matter of principle