Question

SELECT campus,semester, AVG(CountOfStudents)
FROM
(
  SELECT semester,year,campus, count(*) as CountOfStudents
  FROM regestration
  GROUP BY  semester, year, campus,student_id
) t
GROUP BY   campus,semester

我需要做的是找到每个校区每个学期的平均人数

我的表结构是：

表名 - 注册

student_id
campus
year
batch
semester

campus，year，semester和batch这些可以帮助识别唯一记录，而student_id可能会重复，上面的查询会给出错误答案。

Answer 1

请按照以下步骤操作：

从student_ID子句和

GROUP BY

在DISTINCT

COUNT()

查询，

SELECT campus, semester, AVG(CountOfStudents)
FROM
(
  SELECT semester, year, campus, count(DISTINCT student_id) as CountOfStudents
  FROM   registration
  GROUP BY  semester, year, campus
) t
GROUP BY   campus, semester

嵌套查询中的SQL Server查询更正

1 个答案: