MYSQL初阶学习笔记——进阶三：排序查询

#进阶三：排序查询
/*
语法：
    select 查询列表
    from 表
    【where 筛选条件】
    order by 排序列表 【asc|desc】
    ***执行顺序：from->where->select->orderby
特点：
    1.asc为升序，desc为降序，默认为升序
    2.order by子句 可以支持单字段，多字段，表达式，函数，别名
    3.order by子句一般放在查询语句的最后，limit子句除外

*/

#案例1：查询员工信息，要求工资从高到低排序
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>=90的员工信息，按入职时间的先后顺序进行排序【添加筛选条件】
SELECT *
FROM employees
WHERE department_id>=90
ORDER BY hiredate ASC;

#案例3：按年薪高低排序 员工信息【按表达式排序】
SELECT     *,
    salary*12*(1+IFNULL(commission_pct,0))
FROM employees
ORDER BY salary*12*(1+IFNULL(commission_pct,0)) DESC;

#案例4：按年薪高低排序【按别名排序】
SELECT     *,
    salary*12*(1+IFNULL(commission_pct,0)) AS 年薪
FROM employees
ORDER BY 年薪 DESC;

#案例5：按姓名的长度显示员工的姓名和工资【按函数排序】
/*引入 length函数*/
SELECT     last_name,first_name,salary,
    LENGTH(last_name) AS 字节长度
FROM employees
ORDER BY LENGTH(last_name) DESC;

#案例6：查询员工信息，先按工资排序，再按员工编号排序【多字段排序】
SELECT *
FROM employees
ORDER BY salary ASC,employee_id DESC;

#=================Test===============================

#1.查询员工的姓名和部门号和年薪，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8000~17000的员工的姓名和工资，按工资降序
SELECT     last_name,salary
FROM     employees
WHERE    NOT(salary BETWEEN 8000 AND 17000)
ORDER BY salary DESC;

#3.查询邮箱中包含e的员工信息，并先按邮箱字节数降序，再按部门号升序
SELECT     *,LENGTH(email)
FROM     employees
WHERE    email LIKE '%e%'
ORDER BY LENGTH(email) DESC,department_id ASC;