order by 关键字
作用：用于对查询结果进行排序
select * from emp where deptno = 20 order by sal asc /desc;
如何排序之升降问题
*用关键字： sal（升序）select * from emp where deptno = 20 order by sal asc
desc（降序）select * from emp where deptno = 20 order by sal desc;
*sal为默认操作，不写也可以；
如果排序的列值相同时，如何处理？
select * from emp where deptno = 20 order by sal desc,ename desc
*先排整体再排局部