1. CREATE TABLE `employees` (
    2. `emp_no` int(11) NOT NULL,
    3. `birth_date` date NOT NULL,
    4. `first_name` varchar(14) NOT NULL,
    5. `last_name` varchar(16) NOT NULL,
    6. `gender` char(1) NOT NULL,
    7. `hire_date` date NOT NULL,
    8. PRIMARY KEY (`emp_no`));
    9. CREATE TABLE `salaries` (
    10. `emp_no` int(11) NOT NULL,
    11. `salary` int(11) NOT NULL,
    12. `from_date` date NOT NULL,
    13. `to_date` date NOT NULL,
    14. PRIMARY KEY (`emp_no`,`from_date`));

    1.select e.emp_no,s.salary,e.first_name,e.last_name
    from employees as e
    join salaries as s
    on e.emp_no = s.emp_no
    2.当前
    where s.to_date=’9999-01-01’
    3.第二多
    select max(salary)
    from salaries
    where salary<
    (select max(salary) from salaries)