11.获取所有员工当前的manager

获取所有员工当前的manager，如果当前的manager是自己的话结果不显示，当前表示to_date='9999-01-01'。结果第一列给出当前员工的emp_no,第二列给出其manager对应的manager_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 `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`));

解析：考察表的连结

select emp.emp_no, man.emp_no as manager_no
from dept_emp as emp, dept_manager as man
where emp.dept_no = man.dept_no
and emp.emp_no != man.emp_no
and emp.to_date = '9999-01-01'
and man.to_date = '9999-01-01';