case when的疑问

[OSHAPPY]

数据库里有1,2,3,4,5共5条记录,要用一条sql语句让其排序,使它排列成4,5,1,2,3
第一种：
select * from o
order by case id when 4 then 1
when 5 then 2
when 1 then 3
when 2 then 4
when 3 then 5 end
第二种：
select * from o
order by case when id = 4 then 1 end,
case when id = 5 then 2 end,
case when id = 1 then 3 end,
case when id = 2 then 4 end,
case when id = 3 then 5 end
第一种方式可以实现功能,但第二种方式却不能,为什么？这两种方式有什么区别？？？

[百年树人]

第二种

select * from o  
order by 
 case 
  when id = 4 then 1 
  when id = 5 then 2 
  when id = 1 then 3 
  when id = 2 then 4
  when id = 3 then 5 
 end 

[百年树人]

还有一种方法

select * from o  
order by 
  charindex(','+ltrim(id)+',',',4,5,1,2,3,')

[OSHAPPY]

不是很明白,为什么去掉end就可以了？

[以学习为目的]

--正确
select * from o  
order by 
 case 
  when id = 4 then 1 
  when id = 5 then 2 
  when id = 1 then 3 
  when id = 2 then 4
  when id = 3 then 5 
 end 

--错误
select * from o  
order by case when id = 4 then 1 end,--end当id<>4时，语句就停止了
 case when id = 5 then 2 end,
 case when id = 1 then 3 end,
 case when id = 2 then 4 end,
 case when id = 3 then 5 end  

[OSHAPPY]

明白啦,谢谢