Question

SELECT 
    departments.department_id,
    department_name,
    departments.manager_id,
    first_name,
    max(salary) as Maximum_Salary,
    min(salary) Minimum_Salary 
FROM departments,employees 
WHERE departments.department_id = employees.department_id
    AND departments.manager_id = employee_id 
GROUP BY departments.department_id, department_name, 
    departments.manager_id, first_name
ORDER BY department_id;

SELECT
    departments.department_id,
    department_name,
    departments.manager_id,
    max(salary) as Maximum_Salary,
    min(salary) Minimum_Salary 
FROM departments,employees 
WHERE departments.department_id = employees.department_id 
GROUP BY departments.department_id, department_name, departments.manager_id
ORDER BY department_id;

我尝试过两次查询。我每次都得到经理的工资，而不是部门的最高和最低工资，但是如果我从第一个查询中删除'first_name'并修改join子句，那么答案是对的（即第二个查询），但我想得到经理的名字。

Answer 1

您需要选择员工表，如下所示： employees.salary 和 employees.first_name 。

查询将如下所示：

select departments.department_id,department_name,departments.manager_id,employees.first_name,max(employees.salary) as Maximum_Salary,min(employees.salary) Minimum_Salary from departments,employees where departments.department_id=employees.department_id and departments.manager_id=employee_id group by departments.department_id,department_name,departments.manager_id,first_name order by department_id;

Answer 2

您必须为employees表创建两个JOIN：首先在employee和manager_id之间进行联接，然后在employee和department_id之间进行第二次联接。

这样的事情应该有效：

SELECT 
    d.department_id,
    d.department_name,
    d.manager_id,
    m.first_name,
    max(e.salary) as Maximum_Salary,
    min(e.salary) Minimum_Salary
FROM departments d
LEFT JOIN employees e ON d.department_id=e.department_id
LEFT JOIN employees m ON d.manager_id = m.employee_id
GROUP BY d.department_id, d.department_name, 
    d.manager_id, m.first_name
ORDER BY d.department_id;

Answer 3

您可以使用外部申请按部门ID获取最低和最高工资，并将其应用于经理信息。

SELECT  d.department_id,
        d.department_name,
        d.manager_id,
        m.first_name,
        s.Maximum_Salary,
        s.Minimum_Salary
FROM    departments d
        INNER JOIN employees m ON m.employee_id = d.manager_id
        OUTER APPLY (SELECT MAX(salary) Maximum_Salary,
                            MIN(salary) Minimum_Salary
                     FROM   employees e
                     WHERE  e.department_id = d.department_id
        ) s
ORDER BY d.department_id

如果您的dbms不支持外部应用..左连接也将起作用

SELECT  d.department_id,
        d.department_name,
        d.manager_id,
        m.first_name,
        s.Maximum_Salary,
        s.Minimum_Salary
FROM    departments d
        INNER JOIN employees m ON m.employee_id = d.manager_id
        LEFT JOIN (SELECT   e.department_id,
                            MAX(salary) Maximum_Salary,
                            MIN(salary) Minimum_Salary
                   FROM     employees e
                   GROUP BY e.department_id
                  ) s ON s.department_id = d.department_id
ORDER BY d.department_id

如何获得所有部门的最高和最低工资以及每个部门的部门名称，经理ID，经理姓名？

3 个答案: