SQL Server - 在同一查询中获取带有过滤器和不带过滤器的计数（*）答案

【问题标题】：SQL Server - Get count(*) with filter and without filter in same querySQL Server - 在同一查询中获取带有过滤器和不带过滤器的计数（*）
【发布时间】：2020-11-11 09:45:27
【问题描述】：

在下面的查询中，我试图按部门统计所有 FTE 学生，为此我使用了过滤器 U.[IsFullTimeStudent] = 1。

在同一个结果集中，我还想获取部门中学生的TotalCount，这意味着需要删除过滤器U.[IsFullTimeStudent] = 1。

SELECT 
    S.[DepartmentId], COUNT(U.[StudentId]) AS TotalFTEStudents
FROM 
    [dbo].User U
INNER JOIN 
    dbo.[Student] S ON U.[UserId] = S.[UserId]
INNER JOIN 
    [dbo].Department D ON D.[DepartmentId] = S.[DepartmentID]
WHERE 
    D.[CollegeId] = 3 AND U.[IsFullTimeStudent] = 1
GROUP BY 
    S.[DepartmentId]

简而言之，我的结果集应该返回 DepartmentId、TotalFTEStudents 和 TotalStudents

【问题讨论】：

标签： sql-server join filter

【解决方案1】：

使用条件聚合：

SELECT S.DepartmentId,
       COUNT(CASE U.IsFullTimeStudent WHEN 1 THEN 1 END) AS FullTimeStudents,
       COUNT(U.StudentId) AS TotalFTEStudents
FROM dbo.[User] U --USER is a Reserved Keyword, but this was one of the few objects that wasn't delimit identified. This statement would never have run
                  --Though I suggest fixing the name; don't use Reserved Keywords for object names.
     INNER JOIN dbo.Student S ON U.UserId = S.UserId
     INNER JOIN dbo.Department D ON D.DepartmentId = S.DepartmentID
WHERE D.CollegeId = 3
GROUP BY S.DepartmentId;

【讨论】：