题解 | #统计各个部门的工资记录数#

SELECT
    d.dept_no,
    d.dept_name,
    COUNT(*) AS sum 
FROM
    dept_emp AS de
    JOIN salaries AS s ON de.emp_no = s.emp_no
    JOIN departments AS d ON de.dept_no = d.dept_no 
GROUP BY
    d.dept_no 
ORDER BY
    d.dept_no

** 思路 **

1. 先把员工表和薪水表连接起来形成员工薪水表
2. 把员工薪水表和部门表联合起来
3. 根据部门表中的dept_no字段进行group by
4. 使用SUM函数对group by 进行统计
5. 对整个查询结果进行排序