内部连接和 Avg( ) 函数

Question

我正在使用 sql-server.I table 看起来像

StudentName   Class  score
Jim            a1     80
Ann            a1     83
Bill           a2     90

我想要 select 个成绩高于 his/her class 平均分的学生。这是我的代码：

Select a.StudentName
From Table a
inner Join Table b
On a.score>(select avg(b.score) From b
Where a.class=b.class 
group by class);

我认为"where a.class=b.class"中可能存在一些问题，请问我的内部连接方法是否正确？我也可以使用 join 吗？

Answer 1

您需要将 Table b(items) 添加到您的 SELECT
喜欢 b.score , b.class

Answer 2

尝试这样的事情：

 Select a.StudentName, TableAvg.class, a.score
  From TableA a
  inner Join  (select class, avg(score) as AvgScore
        From TableA 
        group by class)  TableAvg
  On a.score >  TableAvg.AvgScore
  and a.class = TableAvg.class

未经测试的代码...

Answer 3

示例数据：

SELECT 'Jim' AS StudentName, 'A1' AS Class, 80 AS Score
INTO #Temporary
UNION ALL
SELECT 'Ann', 'A1', 83
UNION ALL
SELECT 'Bill', 'A2', 90

实际查询（无需加入table两次）

SELECT *
FROM (
    SELECT StudentName, Class, Score, AVG(CAST(Score AS FLOAT)) OVER(PARTITION BY Class) AS AvgScore
    FROM #Temporary
) AS T
WHERE T.Score >= T.AvgScore

内部连接和 Avg( ) 函数

Inner join and Avg( ) function

sql

sql-server

average

inner-join