CREATE TABLE `employees` (`emp_no` int(11) NOT NULL,`birth_date` date NOT NULL,`first_name` varchar(14) NOT NULL,`last_name` varchar(16) NOT NULL,`gender` char(1) NOT NULL,`hire_date` date NOT NULL,PRIMARY KEY (`emp_no`));CREATE TABLE `salaries` (`emp_no` int(11) NOT NULL,`salary` int(11) NOT NULL,`from_date` date NOT NULL,`to_date` date NOT NULL,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)
