create table tbGuestBook(BookNameId varchar(8),[Message] varchar(20))
insert into tbGuestBook
select '[军事]','aaaaaa1' union all
select '[军事]','ddaadassd1' union all
select '[军事]','ffff1' union all
select '[博文]','ffggghhhh3' union all
select '[博文]','ffggghhhh3' union all
select '[博文]','dffd3' union all
select '[健康]','tttefff5' union all
select '[健康]','ffggghhhh5' union all
select '[文物]','dsfdsfdsf6' union all
select '[文物]','ffggghhhh6' union all
select '[其他]','eeeeeeee8' union all
select '[其他]','ddddddd8' union all
select '[其他]','sfdfdfsd8' union all
select '[其他]','fgghf8' union all
select '[其他]','dfgdf8' 


select BookNameId,
stuff((select ','+[Message] 
from tbGuestBook where BookNameId = e.BookNameId 
for xml path('')),1,1,'') as BookNameList from tbGuestBook E
group by BookNameId

/*
BookNameId BookNameList
---------- ---------------------------------------------
[博文]       ffggghhhh3,ffggghhhh3,dffd3
[健康]       tttefff5,ffggghhhh5
[军事]       aaaaaa1,ddaadassd1,ffff1
[其他]       eeeeeeee8,ddddddd8,sfdfdfsd8,fgghf8,dfgdf8
[文物]       dsfdsfdsf6,ffggghhhh6
*/

--加上top 2 不就ok了吗？
select BookNameId,
stuff((select top 2 ','+[Message] 
from tbGuestBook where BookNameId = e.BookNameId 
for xml path('')),1,1,'') as BookNameList from tbGuestBook E
group by BookNameId

/*
BookNameId BookNameList
---------- -----------------------------
[博文]       ffggghhhh3,ffggghhhh3
[健康]       tttefff5,ffggghhhh5
[军事]       aaaaaa1,ddaadassd1
[其他]       eeeeeeee8,ddddddd8
[文物]       dsfdsfdsf6,ffggghhhh6
*/