MySQL 进阶3 排序查询

#进阶3 排序查询 格式:

 select 查询列名
  from 表
  [where 筛选条件]
  order by 排序列名 [asc / desc]    

排序查询/嵌套排序查询/函数查询/[按别名进行 排序]/  [按表达式排序] /[按多个字段]

#进阶3 排序查询/
/*
  select 查询列名
  from 表
  [where 筛选条件]
  order by 排序列名 [asc / desc]
*/
# 案例2: 查询部门编号>=90 的员工信息,按入职时间先后进行排序
SELECT *
FROM employees
WHERE department_id >=90
ORDER BY hiredate;

#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 [按别名进行 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]: 举例length()
SELECT LENGTH(last_name) 字节长度,last_name,salary
FROM employees
ORDER BY LENGTH(last_name) DESC; 

#案例6: 查询员工信息,要求先按工资升序,若重复再按员工编号降序[按多个字段]
SELECT *
FROM employees
ORDER BY salary ,employee_id DESC;