双top的问题

SQL code

declare  @table1 table (id int)insert into @table1select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 ;witha as (    select top(5)id from @table1)select top(1)id from a order by id desc

应该以上语句输出为结果5，但是实际结果为8，请问大侠这个是为什么？下面的语句结果也是一样的

SQL code

select top(1)id from( select top(5)id from @table1) a order by id desc

[解决办法]

SQL code

declare  @table1 table (id int)insert into @table1select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 ;witha as (    select top(5)id from @table1 order by id)select top(1)id from a order by id desc/*(8 行受影响)id-----------5(1 行受影响)*/