MySql进阶3：排序查询

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MySql进阶3：排序查询

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#MySql进阶3：排序查询
/*
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升序 / desc降序]

特点：
	1.asc代表升序，desc代表降序
	如果不写，默认是升序
	2.order by句中，可以支持单个字段、多个字段、表达式、函数、别名
	3.order by子句一般放在查询语句的最后面，limit子句除外
*/

#案例1：查询员工信息，要求工资从高到低
SELECT
  *
FROM
  employees
ORDER BY salary DESC;

SELECT
  *
FROM
  employees
ORDER BY salary ASC;

#案例2：查询部门编号>=90的员工信息，按照入职时间的先后进行排序[添加筛选条件]
SELECT
  *
FROM
  employees
WHERE `department_id` >= 90
ORDER BY hiredate ASC;

#案例3：按年薪的高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：按年薪的高低显示员工的信息和年薪,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length
SELECT
  LENGTH (last_name) AS 字节长度,
  last_name,
  salary
FROM
  employees
ORDER BY 字节长度 DESC;

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