聚合函数并在 2 个条件下加入

Question

我有 Oracle 的这个任务。它要求我显示部门名称（部门是一个包含该表的 manager_id、department_id 和部门名称的表）、该部门的 manager_id、经理的姓名（在雇员表中找到）和该部门的平均工资（每个员工的工资也可以在员工中找到）。一旦我尝试检索经理姓名（我想通过将他的部门 ID 与员工的 ID 进行比较），它就会弄乱我的平均值。没有它（如下所示）它工作得很好

SELECT d.department_name, AVG(e.salary) as "Salaries"
FROM   employees e join departments d on e.department_id=d.department_id
WHERE  d.manager_id=e.employee_id
GROUP BY e.department_id, d.department_name,d.manager_id
ORDER BY AVG(e.salary)

谁能帮我解决这个问题，或者解释一下我为什么搞砸了？

Answer 1

WITH factoring 子句选择平均工资；然后将其连接到其他表

SQL> with avgsal as
  2    (select e.department_id, round(avg(e.salary)) avg_sal
  3     from employees e
  4     group by e.department_id
  5    )
  6  select d.department_id,
  7         d.department_name,
  8         m.last_name manager,
  9         a.avg_sal
 10  from departments d
 11  join employees m on m.department_id = d.department_id
 12       and m.employee_id = d.manager_id
 13  join avgsal a on a.department_id = d.department_id
 14  order by a.avg_sal;

DEPARTMENT_ID DEPARTMENT_NAME      MANAGER                      AVG_SAL
------------- -------------------- ------------------------- ----------
           50 Shipping             Fripp                           3476
           30 Purchasing           Raphaely                        4150
           10 Administration       Whalen                          4400
           60 IT                   Hunold                          5760
           40 Human Resources      Mavris                          6500
          100 Finance              Greenberg                       8601
           80 Sales                Russell                         8956
           20 Marketing            Hartstein                       9500
           70 Public Relations     Baer                           10000
          110 Accounting           Higgins                        10154
           90 Executive            King                           19333

11 rows selected.

SQL>

快速检查 2 个部门：

SQL> select department_id, round(avg(salary)) avg_sal, count(*) "# of employees"
  2  from employees
  3  where department_id in (20, 30)
  4  group by department_id
  5  order by 1;

DEPARTMENT_ID    AVG_SAL # of employees
------------- ---------- --------------
           20       9500              2
           30       4150              6

SQL>

Answer 2

在查询的经理姓名选择中引入相关子查询。

SELECT d.department_name,
       AVG(e.salary) AS "Salaries",
       (SELECT first_name
               ||' '
               ||last_name
        FROM   employees i
        WHERE  i.employee_id = d.manager_id) AS manager_name
FROM   employees e
       join departments d
         ON e.department_id = d.department_id
GROUP  BY e.department_id,
          d.department_name,
          d.manager_id
ORDER  BY Avg(e.salary);