Question

我已经运行了一个查询，以便向我提供每所学校内的学生总数，但现在我需要知道每所学校内学生的姓名，同时保持最高结果总数位于顶部。如何添加到此查询以显示学生的姓名？

以下是我要向我展示每所学校的学生总数：

SELECT 
   dbo_Schools.Schools, 
   Count(dbo_tStudent.Student) AS NumberOfStudents
FROM 
   dbo_tStudent 
      INNER JOIN dbo_tSchools ON dbo_tStudent.SchoolID=dbo_tSchool.SchoolID
GROUP BY dbo_tSchool.School
ORDER BY Count(dbo_tStudent.Student) DESC;

重要的是，在列出学生的同时，让学生按照最多学生的顺序排列。

Answer 1

在这种情况下，您可以使用Sub Query来实现结果集。

要在子查询中使用order by，您还需要一个top or limit运算符。

SELECT sc.schoolname
    ,st.columns...
FROM dbo_tStudent st
INNER JOIN (
    SELECT TOP 1000 dbo_Schools.SchoolID
        ,min(schoolname) schoolname
        ,Count(dbo_tStudent.Student) AS NumberOfStudents
    FROM dbo_tStudent
    INNER JOIN dbo_tSchools ON dbo_tStudent.SchoolID = dbo_tSchools.SchoolID
    GROUP BY dbo_tSchool.School
    ORDER BY Count(dbo_tStudent.Student) DESC
    ) sc ON st.SchoolID = sc.SchoolID

Answer 2

假设您使用的是SQL Server，您可以使用CTE加入第一个聚合，其中包含以下详细信息：

;WITH cte as (
    SELECT TOP 1000 dbo_Schools.SchoolID, Count(dbo_tStudent.Student) AS NumberOfStudents
    FROM 
        dbo_tStudent 
            INNER JOIN dbo_tSchools ON dbo_tStudent.SchoolID = dbo_tSchools.SchoolID
    GROUP BY dbo_tSchool.School
    ORDER BY Count(dbo_tStudent.Student) DESC
)

SELECT
    sc.<your school name column>,
    st.<your student columns>
from
    dbo_tStudent st
        INNER JOIN cte ON st.SchoolID = cte.SchoolID
        INNER JOIN dbo_tSchools sc on cte.SchoolID = sc.SchoolID

更一般地说：您需要一个derived table（包含group by子句的聚合），它与学生详细信息的select语句一起加入。在此示例中，CTE基本上是SQL Server功能，便于使用派生表。

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