两个聚合函数分组

Question

我正在尝试打印所有工资总和大于部门平均总和的部门名称。

SELECT d.department_name, SUM(e.salary)
FROM departments d, employees e
WHERE d.department_id = e.department_id
GROUP BY d.department_name
HAVING SUM(e.salary) > (SELECT AVG(SUM(salary)) from employees);

在第二次选择之后，我必须按AVG(SUM(salary)) 分组吗？

Answer 1

您需要重复条件中的第一个查询。这可以通过 WITH 子句来完成。

WITH dept_sums AS (SELECT d.department_name, SUM(e.salary) sum_salary
FROM departments d, employees e
WHERE d.department_id = e.department_id
GROUP BY d.department_name)

SELECT * FROM dept_sums d_s_1 WHERE d_s_1.sum_salary > (SELECT AVG(sum_salary) FROM dept_sums d_s_2);

Answer 2

这是窗口（分析）函数派上用场的地方。下面我使用AVG()作为解析函数来计算所有部门的平均总工资。

SELECT department_name, dept_salary FROM (
    SELECT d.department_name, SUM(e.salary) AS dept_salary
         , AVG(SUM(e.salary)) OVER ( ) AS avg_dept_salary
      FROM departments d INNER JOIN employees e
        ON d.department_id = e.department_id
     GROUP BY d.department_name
) WHERE dept_salary > avg_dept_salary;