排序：Order by
select * from company order by salary asc; 升序
select * from company order by name, salary asc; 这里升序以第一个（name）为主
select * from company order by name desc; 降序
选取想要的数据：Limit
从第一位开始提取6个记录：
select * from company limit 6;
从第三位开始提取 2 个记录:
select * from company limit 3 offset 2;
