SQL 服务器 - 根据条件从查询结果集中排除记录

Question

使用以下查询，我试图获得每个部门的 FTE 学生平均人数，每个部门的学生总数除以该部门的 FTE 学生总数。

在少数院系中没有 FTE 学生，为此我使用案例陈述将平均值视为 0，在这种情况下没有 FTE 学生(CASE U.[IsFTEStudent] WHEN 1 THEN 1 END)=0 THEN 0

SELECT D.[DepartmentId],
    CASE WHEN COUNT(CASE U.[IsFTEStudent] WHEN 1 THEN 1 END)=0 THEN 0
    ELSE COUNT(S.[StudentId])/COUNT(CASE U.[IsFTEStudent] WHEN 1 THEN 1 END) END AS 'AverageOfFTEStudents'
    FROM dbo.[Student] S
    INNER JOIN [dbo].User U
    ON S.[StudentId] = U.[UserId]
    INNER JOIN dbo.[Department] D
    ON D.DepartmentId = S.[DepartmentId]
    WHERE D.CollegeId = 5
    GROUP BY S.DepartmentId

以上查询给出的结果即使平均为 0，现在我想排除那些平均 FTE 学生为 0 的部门，这意味着没有 FTE 学生。

简而言之'AverageOfFTEStudents'为0的部门应该从我的结果中排除

Answer 1

我想你想要一个 having 子句；您可以使用 AVG():

简化计算逻辑

SELECT S.[DepartmentId],
    AVG(CASE WHEN [IsFTEStudent] = 1 THEN 1.0 ELSE 0 END) AS [AverageOfFTEStudents]
FROM dbo.[Student] S
INNER JOIN [dbo].User U ON ON S.[StudentId] = U.[UserId]
INNER JOIN dbo.[Department] D ON D.DepartmentId = S.[DepartmentId]
WHERE D.CollegeId = 5
GROUP BY S.DepartmentId
HAVING SUM(CASE WHEN [IsFTEStudent] = 1 THEN 1 ELSE 0 END) > 0

根据 IsFTEStudent 的实际数据类型和值，我们或许可以稍微简化聚合表达式。例如，如果它是具有 0/1 值的整数，则：

SELECT S.[DepartmentId],
    AVG([IsFTEStudent] * 1.0) AS [AverageOfFTEStudents]
FROM dbo.[Student] S
INNER JOIN [dbo].User U ON ON S.[StudentId] = U.[UserId]
INNER JOIN dbo.[Department] D ON D.DepartmentId = S.[DepartmentId]
WHERE D.CollegeId = 5
GROUP BY S.DepartmentId
HAVING SUM([IsFTEStudent]) > 0

SQL 服务器 - 根据条件从查询结果集中排除记录

SQL Server - Exclude records from query result set based on condition

sql

sql-server

average

aggregate-functions

having-clause