题目描述：查找所有员工入职时候的薪水情况，

给出emp_no以及salary， 并按照emp_no进行逆序(请注意，一个员工可能有多次涨薪的情况)
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）方法1

select e.emp_no,s.salary from employees e

left join salaries s

on e.emp_no=s.emp_no and e.hire_date=s.from_date

order by e.emp_no desc

（2）方法2

select a.emp_no,b.salary

from employees as a

left join salaries as b

on a.emp_no=b.emp_no

where a.hire_date=b.from_date and salary is not null

order by a.emp_no desc

;

（3）方法3

SELECT e.emp_no, s.salary

FROM employees AS e

INNER JOIN salaries AS s

ON e.emp_no = s.emp_no AND e.hire_date = s.from_date

ORDER BY e.emp_no DESC

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