mysql 没有给出想要的结果

Question

我正在执行此查询。

select (select FollowersCount from webanalysis.DataTwUser_followers_history where DataTwUserID='80943' and Date <='2015-01-12' order by Date desc limit 1) - (select FollowersCount from webanalysis.DataTwUser_followers_history where DataTwUserID='80943' and Date >='2014-12-12' order by Date  limit 1) as new;

它给了我“18446744073709551606”作为答案，但我想要“-9”作为答案。

如果我执行这个查询1，

select FollowersCount from webanalysis.DataTwUser_followers_history where DataTwUserID='80943' and Date <='2015-01-12' order by Date desc limit 1;

它会给我“193”作为答案。如果执行此查询2

select FollowersCount from webanalysis.DataTwUser_followers_history where DataTwUserID='80943' and Date >='2014-12-12' order by Date  limit 1;

它会给我“202”作为答案，所以我想这样做，

193 - 202 = -9。

我哪里错了？需要帮助。

Answer 1

你有无符号整数值，你正在做减法，MySQL将结果限制为无符号整数......该值溢出(下溢)下限，并“换行”。

要解决此问题，请在减法之前将无符号值转换或转换为有符号值。

SELECT CAST(( val1 ) AS SIGNED) - CAST(( val2 ) AS SIGNED) AS foo

(用返回无符号整数值的子查询替换 val1 和 val2)

如果您愿意，可以使用 CONVERT 函数代替 CAST

SELECT CONVERT(( val1 ),SIGNED) - CONVERT(( val2 ),SIGNED) AS foo