SQL查詢列表那些低於平均

Question

我有以下格式2個表格更高：

• 員工（僱員，EmployeeName，DepartmentID的）
• 部門（DepartmentID的，DEPTNAME）

在每個部門工作的僱員人數多於部門僱員人數的平均數。

即時通訊尋求結果的格式如下：

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

Answer 1

，因爲員工可以在只有一個部門，員工的平均數量就是部門總數中員工總數。所以如何：

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)) 

Answer 2

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，您可以使用分析功能，這是更優雅：

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