sql笔记-group by 统计功能

 --查询月销售量小于20的人员销售情况
 SELECT C.Category,
        SUM(c.[Count]) AS CategorySum
 FROM   test.dbo.Category c
        --WHERE c.Category IN ('A','C')
 GROUP BY
        C.Category
 HAVING SUM(c.[Count]) < 20
 ORDER BY
        CategorySum

 --查询每门课的最低分
 SELECT C.Category,
        MIN(C.[Count]) AS CategoryMinCount
 FROM   test.dbo.Category c
 GROUP BY
        C.Category

 --搜索名字相同的学生
 SELECT s.Sname,
        COUNT(s.Sname)
 FROM   Stu s
 GROUP BY
        s.Sname
 HAVING COUNT(s.Sname) > 1

 --每个年龄的人数
 SELECT
     s.Age
     ,COUNT(s.Age) AS AgeCount
 FROM test.dbo.Stu s
 GROUP BY s.Age

 --年龄段统计
 SELECT t1.AgeRange,
        COUNT(*) AS AgeRangePeopleCount
 FROM   (
            SELECT Sno,
                   CASE
                        WHEN (age > 50) THEN 'gt100'
                        WHEN (age > 20 AND age <= 50) THEN '20-30'
                        WHEN (age <= 20) THEN '10-20'
                   END AS AgeRange
            FROM   test.dbo.Stu s
        ) t1
 GROUP BY
        t1.AgeRange