获取所有员工当前的manager

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 `dept_manager` (
`dept_no` char(4) NOT NULL,
`emp_no` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`dept_no`));

select de.emp_no,dm.emp_no manager_no from dept_emp de left join dept_manager dm on de.dept_no = dm.dept_no where de.to_date= '9999-01-01' and dm.to_date = '9999-01-01' and de.emp_no != dm.emp_no