SQL 排序



我想请问.第一列中的日期有null值,我想把null值排序在最前,并把有数据的从大到小排序. 怎么实现/.
[解决办法]
select *
from tb
order by case when receipt_time is null then 0 else 1 end,receipt_time desc
[解决办法]
isnull(A,B) A:列名 B:替换值

[解决办法]
默认null就是排最上

----------------------------
-- Author  :DBA_Huangzj()
-- Date    :2013-07-25 09:44:10
-- Version:
--      Microsoft SQL Server 2014 (CTP1) - 11.0.9120.5 (X64) 
--Jun 10 2013 20:09:10 
--Copyright (c) Microsoft Corporation
--Enterprise Evaluation Edition (64-bit) on Windows NT 6.2 <X64> (Build 9200: ) (Hypervisor)
--
----------------------------
--> 测试数据：[huang]
if object_id('[huang]') is not null drop table [huang]
go 
create table [huang]([a] int,[b] int)
insert [huang]
select null,1 union all
select null,2 union all
select 3,4
--------------开始查询--------------------------

select * from [huang]
----------------结果----------------------------
/* 
a           b
----------- -----------
NULL        1
NULL        2
3           4
*/

if object_id('[tb]') is not null drop table tb
go 
create table tb([a] int,[b] int)
insert tb
select null,1 union all
select null,2 union all 
 
select 3,4 union all 
select 2,4 union all
select 5,4

select * 
from tb
order by isnull(a,1000000) desc

create table #A([time] datetime)
insert into #A values ('2013-07-25')
insert into #A values (NULL)
insert into #A values ('2013-07-24')
insert into #A values (NULL)
insert into #A values ('2013-07-26')

select * from #A

select * from #A order by ISNULL([time],'9999-01-01') DESC