SQL获取百分比

Question

我有以下代码来计算PersonType的总死亡率和组。现在我想要一个列来计算每个死亡人数的百分比。即将每个人类的价值除以总死亡人数。

Select distinct persontype as PerSsonType, sum(fatalities_in_crash) as Total_Deaths 

    from [CarCrash].[Source_Data_Staging] 
group by PersonType 

Answer 1

您可以使用ANSI标准的窗口功能（这是大多数数据库，包括SQL Server支持）：

Select persontype as PerSsonType, sum(fatalities_in_crash) as Total_Deaths, 
     sum(fatalities_in_crash) * 1.0/sum(sum(fatalities_in_crash)) over() as ratio 
from [CarCrash].[Source_Data_Staging] 
group by PersonType; 

注意：您几乎不必SELECT DISTINCT与GROUP BY。 * 1.0是因为一些数据库使用整数除法 - 这将产生所有行的0。

Answer 2

可以跨加入这个查询与选择死亡的总和查询不进行分组：

SELECT persontype, 
     SUM(fatalities_in_crash) AS Total_Deaths, 
     SUM(fatalities_in_crash)/all_deaths AS percentage 
FROM  [CarCrash].[Source_Data_Staging] 
JOIN  (SELECT SUM(fatalities_in_crash) AS all_deaths 
      FROM [CarCrash].[Source_Data_Staging]) t 
GROUP BY persontype