sql - Oracle - 如何从子查询中返回平均值？

Question

我需要选择工资高于按部门分组的平均工资的员工。

SELECT * FROM employees
WHERE salary > (SELECT AVG(salary), department_id FROM employees GROUP BY department_id)

它失败了，因为它返回了我 2 列。

我试过这个查询：

SELECT * FROM employees
HAVING salary > AVG(salary)
GROUP BY (department_id)

现在我收到错误消息：ORA-00979: not a GROUP BY expression

Answer 1

最简单的跨数据库方法是使用 JOIN：

SELECT employees.*
FROM employees
JOIN ( SELECT department_id, AVG(salary) avgSalary
       FROM employees
       GROUP BY department_id) departmentSalaries
  ON employees.department_id = departmentSalaries.department_id
  AND employees.salary > departmentSalaries.avgSalary

Oracle 最有效的方法是使用分析函数（又名窗口函数）：

SELECT * FROM (
  SELECT e.*, AVG(e.salary) OVER ( PARTITION BY e.department_id ) as avgSalary
  FROM employees e) t
WHERE salary > avgSalary