SQL獲取百分比

Question

我有以下代碼來計算PersonType的總死亡率和組。現在我想要一個列來計算每個死亡人數的百分比。即將每個人類的價值除以總死亡人數。

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標準的窗口功能（這是大多數數據庫，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：您幾乎不必SELECT DISTINCT與GROUP BY。 * 1.0是因爲一些數據庫使用整數除法 - 這將產生所有行的0。

Answer 2

可以跨加入這個查詢與選擇死亡的總和查詢不進行分組：

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