SQL-26 (二次分组)汇总各个部门当前员工的title类型的分配数目，结果给出部门编号dept_no、dept_name、其当前员工所有的title以及该类型title对应的数目count

题目描述

汇总各个部门当前员工的title类型的分配数目，结果给出部门编号dept_no、dept_name、其当前员工所有的title以及该类型title对应的数目count
CREATE TABLE `departments` (
`dept_no` char(4) NOT NULL,
`dept_name` varchar(40) NOT NULL,
PRIMARY KEY (`dept_no`));
CREATE TABLE `dept_emp` (
`emp_no` int(11) NOT NULL,
`dept_no` char(4) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`dept_no`));
CREATE TABLE IF NOT EXISTS `titles` (
`emp_no` int(11) NOT NULL,
`title` varchar(50) NOT NULL,
`from_date` date NOT NULL,
`to_date` date DEFAULT NULL);

输入描述:

无

输出描述:

dept_no	dept_name	title	count
d001	Marketing	Senior Engineer	1
d001	Marketing	Staff	1
d002	Finance	Senior Engineer	1
d003	Human Resources	Senior Staff	1
d004	Production	Senior Engineer	2
d005	Development	Senior Staff	1
d006	Quality Management	Engineer	2
d006	Quality Management	Senior Engineer	1

SQL:

select A.dept_no,departments.dept_name,A.title,A.count
from departments INNER JOIN(select dept_emp.emp_no, dept_emp.dept_no,t.title,count(t.title) as count
from dept_emp INNER JOIN titles t
on dept_emp.emp_no=t.emp_no and dept_emp.to_date='9999-01-01' and t.to_date='9999-01-01'
GROUP BY dept_emp.dept_no,t.title)as A
WHERE departments.dept_no=A.dept_no

　　最重要的是对其进行二次分组  统计相同部门，相同title 的数目。