需要更正Sql Query

时间:2012-12-25 22:01:08

标签: sql sql-server

我需要一点帮助以下查询。我需要找到:

  

每个校区每学期的平均人数

我的表结构是:

  • 表名 - 注册
    • student_id数据
    • 校园
    • 批次
    • 学期

campusyearsemesterbatch的帮助下,我可以识别每个独特的学期。我的student_id更多地在数据库中重复。

我做了以下但是没有帮助。所以我需要一些帮助。

SELECT semester,year,campus
  FROM regestration
  GROUP BY  semester, year, campus
  ORDER BY count(*) desc

3 个答案:

答案 0 :(得分:0)

尝试类似:

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

答案 1 :(得分:0)

要获得每个学期每个校区的学生人数,您需要在查询中添加COUNT(*):

SELECT semester, year, campus, COUNT(*) as students
    FROM registration
    GROUP BY semester, year, campus

我不知道你想要的平均值。

答案 2 :(得分:0)

怎么样

select avg(students), campus from (
  select count(student_id) students, campus from registration
   group by semester, year, campus
) group by campus