在计算百分比时将 Over() 与聚合函数一起使用

Question

我正在编写一个查询来打印大学每个系的学生总数，我还想打印每个系的学生占大学学生总数的百分比。

select dep.[Id] as DepId, dep.[Name] as Department, COUNT(s.[Id]) as [TotalStudents]
    , COUNT(S.[Id]) * 100/NULLIF(COUNT(COUNT(S.[Id]) OVER(), 0) AS [Percentage]
from dbo.[Department] dep
left join dbo.[student] s on dep.[Id] = s.[DepartmentId]
group by dep.[Id], dep.[Name]

在计算百分比时出现问题，上述查询抛出错误

dbo.Student.Id is invalid in the select list because it is not contained in either an aggregate function.

如果所有部门共有 10 名学生，而 Dep1 有 5 名学生，则百分比应为 50。

Answer 1

您可以使用这样的 window 函数，但是您需要 window SUM 个计数，而不是 window COUNT()。我还建议在计算中放入一个小数值，以避免整数除法：

select d.[Id] as DepId, d.[Name] as Department, 
    count(s.[Id]) as [TotalStudents], 
    count(s.[Id]) * 100.0 / nullif(sum(count(s.[Id])) over(), 0) AS [Percentage]
from dbo.[Department] d
left join dbo.[student] s on d.[Id] = s.[DepartmentId]
group by d.[Id], d.[Name]

在计算百分比时将 Over() 与聚合函数一起使用

Using Over() with aggregate functions while calculating percentage

sql

sql-server

count

aggregate-functions

percentage