/*
引入：select * from employees
语法：select 查询列表 from 表 【where 筛选条件】order by 排序列表 【asc|desc】
特点：默认升序asc order by后面可以接别名、单个或多个字段、表达式、函数
order by 一般放在查询语句的最后面，limit子句除外
order by（本节中执行顺序在第四位（最后））
*/

案例1：查询员工信息，要求工资从高到低排序

use myemployees;
show tables;
select * from employees order by salary desc;
select * from employees order by salary asc;
select * from employees order by salary;

案例2：查询部门编号大于等于90的员工信息，按入职时间的先后进行排序

select * from employees where department_id>=90 order by hiredate asc;

案例3：按年薪的从高到低显示员工的信息和年薪【按表达式排序】

select *,salary*12*(1+ifnull(commission_pct,0)) as 年薪 from employees order by 
salary*12*(1+ifnull(commission_pct,0)) desc;

案例4：按姓名的长度显示员工的姓名和工资【按函数、别名排序】

select length(concat(last_name,first_name)) as 姓名长度,concat(last_name,first_name) 
as 姓名,salary from employees order by 姓名长度 desc;

案例5：查询员工信息，先按工资升序，再按员工编号降序[按多个字段排序]

select * from employees order by salary asc,employee_id desc;

测试

1.查询员工的姓名和部门编号和年薪，按年薪降序 按姓名升序

select last_name,department_id,salary*12*(1+ifnull(commission_pct,0)) as 年薪 from 
employees order by 年薪 desc,last_name asc;

2.选择工资不在8000到17000的员工的姓名和工资，按工资降序

select last_name,salary from employees where salary not between 8000 and 17000 order by 
salary desc;

3查询邮箱中包含e的员工信息，并先按邮箱的字节数降序，再按部门号升序

department_id asc;
#