Question

我有以下格式的2个表：

employee（employeeID，EmployeeName，DepartmentID）
部门（DepartmentID，DeptName）

在每个部门工作的员工中，有多少员工的员工人数超过部门员工的平均员工人数。

我以下列格式查看结果：

Dept Name   | Num of Emp
engineering | 10
science     | 15

Answer 1

SELECT  deptName, cnt
FROM    (
        SELECT  departmentID, COUNT(*) AS cnt
        FROM    employee
        GROUP BY
                departmentID
        HAVING  COUNT(*) >=
                (
                SELECT  AVG(cnt)
                FROM    (
                        SELECT  COUNT(*) AS cnt
                        FROM    employee
                        GROUP BY
                                departmentID
                        )
                )
        ) e
JOIN    departments d
ON      d.departmentID = e.departmentID

在Oracle中，您可以使用更优雅的分析函数：

SELECT  DeptName, cnt
FROM    (
        SELECT  q.*, AVG(cnt) OVER() AS acnt
        FROM    (
                SELECT  departmentID, COUNT(*) AS cnt
                FROM    employee
                GROUP BY
                        departmentID
                ) q
        ) e
JOIN    departments d
ON      d.departmentID = e.departmentID
WHERE   cnt >= acnt

Answer 2

由于员工只能在一个部门，因此员工的平均数量就是员工总数超过部门总数。那怎么样：

SELECT    dept.name, COUNT(emp.id) AS employeeCount
FROM         emp INNER JOIN dept ON emp.deptId = dept.id
GROUP BY dept.name
HAVING      (COUNT(emp.id) >
(SELECT  COUNT(*) FROM emp) /
(SELECT     COUNT(*) FROM dept))

SQL查询列表高于平均值的那些

2 个答案: