Question

  SELECT d.DEPARTMENT_NAME 
    FROM Department d, 
         Student s 
   WHERE d.DEPARTMENT_ID = s.DEPARTMENT_ID 
GROUP BY d.DEPARTMENT_NAME 
  HAVING COUNT(s.STUDENT_ID) < MAX(COUNT(s.STUDENT_ID));

该代码用于加入学生和部门表。 department_id是部门与学生之间的关键。需要找到没有最大学生人数的部门。错误是组函数嵌套太深。嵌套是否允许最多3个？

这是确切的错误

ORA-00935：群组功能嵌套太深

Answer 1

UPD 。哦，石〜！我刚刚提到了与Oracle有关的问题。我不知道rank()函数的语法，但我认为它应该非常接近Sql Server。

这是：

;with Department(DEPARTMENT_ID, DEPARTMENT_NAME) as (
    select 1, 'first' union all
    select 2, 'second' union all
    select 3, 'third'
)
, Student(STUDENT_ID, DEPARTMENT_ID) as (
    select 1, 1 union all
    select 2, 2 union all
    select 3, 2 union all
    select 4, 2 union all
    select 5, 3 union all
    select 6, 3 union all
    select 7, 3
)
, DepOrdered as (
    select
        d.DEPARTMENT_ID,
        d.DEPARTMENT_NAME,
        s.StudentCnt,
        -- rank departments by the number of students
        rank() over (order by s.StudentCnt desc) as Rnk
    from Department d
    cross apply (
        -- for every department count its students
        select
            count(s.STUDENT_ID) StudentCnt
        from Student s
        where
            d.DEPARTMENT_ID = s.DEPARTMENT_ID
    ) s
)
select
    DEPARTMENT_ID,
    DEPARTMENT_NAME,
    StudentCnt
from DepOrdered
where
    -- Rnk = 1 would have all departments with max number of students
    Rnk > 1

使用join和group by ...给出错误

1 个答案: