Question

下面的这句话为我提供了一些我需要的数据。

select TankName, COUNT(*) as Tanks, sum(Battles) as Battles, 
   SUM(victories) as Victories
from MemberTanks
where Tier = 9 and Class = 'Medium'
group by TankName
order by Tanks desc

我想在结果集中显示胜利的百分比，但我不知道该怎么做。我试过......

select TankName, COUNT(*) as Tanks, sum(Battles) as Battles, 
   SUM(victories) as Victories, SUM(Victories)/SUM(Battles) as Percentage
from MemberTanks
where Tier = 9 and Class = 'Medium'
group by TankName
order by Tanks desc

...但每一行的回报率为“0”。

我怎样才能最好地获得这个价值？

Answer 1

当你计算百分比列，因为SUM（X）返回一个INT值，结果会变为floored，因此返回0作为floored result

将SUM（胜利）乘以像1.0这样的十进制值（以便将一个操作数转换为十进制/数字）然后你会得到正确的结果。

试试这个：

SELECT TankName, 
    COUNT(*) as Tanks, 
    SUM(Battles) as Battles, 
  SUM(victories) as Victories,
    SUM(victories) * 1.0/ SUM(Battles) AS Percentage
 FROM MemberTanks
WHERE Tier = 9 
  AND Class = 'Medium'
GROUP BY TankName
ORDER BY Tanks desc

此外，如果您使用的是SQL Server 2005或更高版本，则可以使用如下所示的CTE减少calculate.computations：

WITH qry AS
(
    SELECT TankName, 
        COUNT(*) as Tanks, 
        SUM(Battles) as Battles, 
        SUM(victories) as Victories
     FROM MemberTanks
    WHERE Tier = 9 
        AND Class = 'Medium'
    GROUP BY TankName
)
SELECT a.*,
                Victories * 1.0 / Battles AS Percentage
  FROM qry a
ORDER BY Tanks DESC

Answer 2

试试这个 -

SUM(Convert(float, Battles))/ Sum(Convert(float, Victories))

请参阅MSDN:

返回参数的数据类型   具有更高的优先权。更多   信息，请参阅数据类型优先级   （处理SQL）。

如果整数除数除以   一个整数除数，结果是一个   具有任何小数部分的整数   截断的结果。

如何划分在select语句中求和的两列？

2 个答案: