标签：使用 包含 取值 interval max weight HERE over mic
1，如何使用
在mysql的编辑器中，可以直接定义 bigint(20) unsigned
2, 发挥的作用
一般默认定义的数据类型为signed（有符号类型），取值返回包含有负数范围，一般正负值的差依然等于无符号类型的范围的上限值。
当定义为unsigned（无符号类型）时， 取值范围仅为正数范围，下限值为0；
3，当设置为unsigned时候，报错BIGINT UNSIGNED value is out of range....如何解决
使用unsigned限制数值范围为正数的时候，如果执行相减操作产生负数；就会报错；解决方法
-- 需要添加四个计算值计算每日变化数据 -- dayConfirmed: 每日确诊 -- dayRecovered: 每日康复 -- dayDeaths: 每日死亡 -- dayExisting: 当日现存 select n.id, n.region_id, n.region_parent_id, n.recovered, n.deaths, n.day_date, n.confirmed, (cast(n.confirmed as signed) - cast(m.confirmed as signed)) as dayConfirmed, (cast(n.recovered as signed) - cast(m.recovered as signed)) as dayRecovered, (cast(n.deaths as signed) - cast(m.deaths as signed)) as dayDeaths, (cast(n.confirmed as signed) - cast(n.recovered as signed) - cast(n.deaths as signed)) as dayExisting from region_data_total as n join region_data_total as m on date_sub(n.day_date, interval 1 day) = m.day_date where n.region_id = m.region_id and n.day_date = (select max(day_date) from region_data_total);
核心： 使用 cast(targetCol as signed) 将所有涉及到的unsigned字段先转化为signed类型后，再进行运算
MYSQL的数据类型（菜鸟教程）：
标签：使用 包含 取值 interval max weight HERE over mic
原文地址：https://www.cnblogs.com/bennyjane/p/12822744.html
