26、汇总各个部门当前员工的title类型的分配数目

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);

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select t1.dept_no,dp.dept_name,t1.title,t1.count
from (
select d.emp_no,d.dept_no,t.title,count(1) as count
from dept_emp d 
inner join titles t on d.emp_no=t.emp_no and d.to_date=‘9999-01-01‘ and t.to_date=‘9999-01-01‘
group by d.dept_no,t.title ) t1
inner join departments dp
on t1.dept_no=dp.dept_no ;