mysql数据库之查询结果排序

1.条件逻辑

select ename,sal,
case when sal <= 2000 then ‘up’
when sal>= 5000 then ‘over’
else ‘ok’
end as status
from emp

2.以指定顺序返回查询结果

select ename,job,sal
from emp
where deptno = 10
order by sal asc
升序是asc 降序是的desc
也可以用数字对应第几列
比如最后一行还可以改写为：order by 3 asc

3.排序时对null的处理

标记两种可能的取值，一种代表null,一种代表非null
eg.非null的升序排列，null放到最后面

select ename,sal,comm
	from(
selcet ename,sal,comm
		case when comm is null then 0 else 1 end as is_null
	from emp
		)x
order by is_nulldesc,comm

4.依据条件逻辑动态调整排序项

如果job等于salesman，就按照comm排序，否则，按照sal排序

select ename,sal ,job,comm
  from emp
  order by case when job = 'salesman' then comm else sal end