SQL - 试图让员工的平均工资高于平均部门工资

Question

我正在尝试获取一个部门的平均工资，然后用它来获取任何高于该平均工资的员工。

我的查询是：

select e.first_name, e.salary, e.department_id from
employees as e
inner join departments as d
on d.id = e.department_id
where salary > (select avg(e.salary)
  from employees as e
  where e.department_id = d.id
  group by e.department_id);

但它只返回一个结果“Ian”。

 first_name | salary | department_id 
------------+--------+---------------
 Ian        |  80000 |             2
(1 row)

        avg         
--------------------
 35000.000000000000
(1 row)

 id | first_name | last_name | salary | department_id 
----+------------+-----------+--------+---------------
  1 | John       | Smith     |  20000 |             1
  2 | Ava        | Muffinson |  10000 |             5
  3 | Cailin     | Ninson    |  30000 |             2
  4 | Mike       | Peterson  |  20000 |             2
  5 | Ian        | Peterson  |  80000 |             2
  6 | John       | Mills     |  50000 |             3
(6 rows)

 id |    name     
----+-------------
  1 | Reporting
  2 | Engineering
  3 | Marketing
  4 | Biz Dev
  5 | Silly Walks
(5 rows)

我做错了什么？ 谢谢！

Answer 1

从一个预查询中的每个部门的薪水开始。这应该是之后所有员工的基础。

select
      e.*,
      JustAvgs.DptAvg
   from
      ( select 
              e.department_id,
              avg(e.salary) DptAvg
           from 
              employees as e
           group by 
              e.department_id) JustAvgs
         JOIN employees e
            on JustAvgs.Department_id = e.Department_ID
           AND e.Salary > JustAvgs.DptAvg

Answer 2

你可以这样做，这里是demo。

select  
    first_name,
    salary,
    department_id
from
(select
    department_id,
    first_name,
    salary,
    avg(salary) over () as avg_salary
from employee
) emp
where salary > avg_salary

输出：

+--------------------------------+
first_name  salary  department_id|
+--------------------------------+
| Ian       80000      2         |
| John      50000      3         |
+--------------------------------+

Answer 3

窗口函数可能是最好的解决方案——就像@zealous 的回答一样。不过，子查询也是很合理的。这个想法是：

select e.first_name, e.salary, e.department_id
from employees as e
where e.salary > (select avg(e2.salary)
                  from employees e2
                  where e2.department_id = e.department_id
                 );

Here 是一个 dbfiddle。

关键思想：

• 您无需将join 转至departments。仅仅因为你有这个想法并不意味着join 是必要的。
• GROUP BY 在子查询中是不必要的。相关性子句负责这一点。