1、查找最晚入职员工的所有信息

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`)); 

select * from employees where hire_date=(select max(hire_date) from employees);
select * from employees order by hire_date desc limit 1;

讨论：https://www.nowcoder.com/questionTerminal/218ae58dfdcd4af195fff264e062138f

2、查找入职员工时间排名倒数第三的员工所有信息
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`));

select * from employees order by hire_date desc limit 2,1;
select * from employees where hire_date = (select hire_date from employees order by hire_date desc limit 2,1);

讨论：https://www.nowcoder.com/questionTerminal/ec1ca44c62c14ceb990c3c40def1ec6c

3、查找各个部门当前(to_date=\’9999-01-01\’)领导当前薪水详情以及其对应部门编号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`));
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`));

select s.* ,d.dept_no
from salaries as s 
join dept_manager as d 
on s.emp_no = d.emp_no
where s.to_date = \'9999-01-01\'
and d.to_date=\'9999-01-01\';

讨论：https://www.nowcoder.com/questionTerminal/c63c5b54d86e4c6d880e4834bfd70c3b

4、查找所有已经分配部门的员工的last_name和first_name
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 `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`));

select e.last_name , e.first_name , d.dept_no
from employees e , dept_emp d
where e.emp_no = d.emp_no;

SELECT ep.last_name, ep.first_name, dp.dept_no 
FROM employees ep 
INNER JOIN dept_emp dp
ON ep.emp_no = dp.emp_no;

讨论：https://www.nowcoder.com/questionTerminal/6d35b1cd593545ab985a68cd86f28671

5、查找所有员工的last_name和first_name以及对应部门编号dept_no，也包括展示没有分配具体部门的员工
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 `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`));

SELECT e.last_name, e.first_name, d.dept_no 
FROM employees e 
LEFT JOIN dept_emp d
ON e.emp_no = d.emp_no;

讨论：https://www.nowcoder.com/questionTerminal/dbfafafb2ee2482aa390645abd4463bf

注意：
　　INNER JOIN 两边表同时有对应的数据，即任何一边缺失数据就不显示。
　　LEFT JOIN 会读取左边数据表的全部数据，即便右边表无对应数据。
　　RIGHT JOIN 会读取右边数据表的全部数据，即便左边表无对应数据。