当字段类型为 unsigned 时，使用相关结果为负值时就会报错，报错如下：
BIGINT UNSIGNED value is out of range in ..
解决方法
使用 cast() 修改字段类型为 signed
select cast(quantity as signed) - cast(frozen_quantity as signed) from ...
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Mysql Query error: BIGINT UNSIGNED value is out of range in..解决方法
原文：http://bstdn.blog.51cto.com/8667020/1951064