汇总各个部门当前员工的title类型的分配数目

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);

select d.dept_no,d.dept_name,title,count(emp_no) count from (select emp_no,d.dept_no,title,dept_name from (select de.emp_no,dept_no,title from dept_emp de,titles t where de.emp_no = t.emp_no and t.to_date = '9999-01-01' and de.to_date = '9999-01-01') t1,departments d where t1.dept_no = d.dept_no) t1,departments d where t1.dept_no = d.dept_no group by t1.dept_no,title

select de.emp_no,dept_no,title from dept_emp de,titles t where de.emp_no = t.emp_no and t.to_date = '9999-01-01' and de.to_date = '9999-01-01'

select emp_no,d.dept_no,title,dept_name from (select de.emp_no,dept_no,title from dept_emp de,titles t where de.emp_no = t.emp_no and t.to_date = '9999-01-01' and de.to_date = '9999-01-01') t1,departments d where t1.dept_no = d.dept_no