mysql-order by子句

得到查询结果后再排序（从磁盘取数据到内存再排序）

select ...
from ...
where ...
order by a -- 按a字段从小到大

order by a -- 按a字段排序,a相等按b排

-- asc -  ascend升序
-- desc - descend降序

order by a asc
order by a desc
order by a desc, b asc

1.薪水从小到大排列

USE hr;
SELECT employee_id,first_name,last_name,salary,job_id,department_id
FROM employees
ORDER BY salary;

2.按部门降序排列，相同部门中，按薪水升序排列

USE hr;
SELECT employee_id,first_name,last_name,salary,job_id,department_id
FROM employees
ORDER BY department_id DESC,salary ASC;

3.薪水大于10000的员工，按姓名排序

USE hr;
SELECT employee_id,first_name,last_name,salary,job_id,department_id
FROM employees
WHERE salary>=10000
ORDER BY first_name,last_name;

注意先过滤后排序，先where(先过滤取数据)后order by(排序)