--> 测试数据：[test]
if object_id('[test]') is not null 
drop table [test]
create table [test](
[id] int,
[UserID] int,
[Value] varchar(2)
)
insert [test]
select 1,100,'AA' union all
select 2,100,'BB' union all
select 3,101,'CC' union all
select 4,100,'DD' union all
select 5,101,'EE'


SELECT *FROM (SELECT DISTINCT [UserID] FROM [test])A
OUTER APPLY(
    SELECT [values]= STUFF(REPLACE(REPLACE(
            (   SELECT value FROM [test] N
                WHERE [UserID] = A.[UserID]
                FOR XML AUTO
             ), '<N value="', ','), '"/>', ''), 1, 1, '')
)N

/*
UserID    values
100    AA,BB,DD
101    CC,EE
*/

------解决方案--------------------

--> 测试数据：[test]
if object_id('[test]') is not null  
drop table [test]
create table [test](
[id] int,
[UserID] int,
[Value] varchar(2)
)
insert [test]
select 1,100,'AA' union all
select 2,100,'BB' union all
select 3,101,'CC' union all
select 4,100,'DD' union all
select 5,101,'EE'

Select Distinct userid,(select value+','  
	from test b where a.userid=b.userid
	for xml path('')) theGroup
From test a