mysql|unsigned 與 signed 類型

通過mysql的數值類型設置，控制數值的正負

1，如何使用

在mysql的編輯器中，可以直接定義 bigint(20) unsigned

 

 

 2, 發揮的作用

一般默認定義的數據類型為signed（有符號類型），取值返回包含有負數范圍，一般正負值的差依然等於無符號類型的范圍的上限值。

當定義為unsigned（無符號類型）時， 取值范圍僅為正數范圍，下限值為0；

3，當設置為unsigned時候，報錯BIGINT UNSIGNED value is out of range....如何解決

使用unsigned限制數值范圍為正數的時候，如果執行相減操作產生負數；就會報錯；解決方法

-- 需要添加四個計算值計算每日變化數據
-- dayConfirmed: 每日確診
-- dayRecovered: 每日康復
-- dayDeaths: 每日死亡
-- dayExisting: 當日現存
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) 將所有涉及到的unsigned字段先轉化為signed類型后，再進行運算

相關內容補充：

MYSQL的數據類型（菜鳥教程）：

• https://www.runoob.com/mysql/mysql-data-types.html