Only one expression can be specified in the select list when the subquery is not introduced with（求助）

BEGIN   TRAN
declare @userName varchar(100)
declare @userSurname varchar(100)
declare @i int
declare @num int
declare @sqlstr nvarchar(1000)
declare @error int
declare @CustomId  varchar(100)

set @i=1
set @num=(select COUNT(*) from (select count(userid) shuliang from dbo.Users group by name,surname having count(userid)>1) as t)
set @userName= (select top 1 name from (select top 1 name,surname from dbo.Users group by name,surname having count(userid)>1 order by name ASC) as t order by name desc)
set @userSurname=(select top 1 surname from (select top 1 name,surname from dbo.Users group by name,surname having count(userid)>1 order by name ASC) as t order by name desc)
set @sqlstr=('select * from User where name="'+CONVERT(varchar(100),@userName)+'" and surname="'+convert(varchar(100),@userSurname)+'" ')
set @i=2
while @i<=@num
begin
set @userName= (select top 1 name from (select top (CONVERT(INT,@i)) name,surname from dbo.Users group by name,surname having count(userid)>1 order by name ASC) as t order by name desc)
set @userSurname=(select top 1 surname from (select top (CONVERT(INT,@i)) name,surname from dbo.Users group by name,surname having count(userid)>1 order by name ASC) as t order by name desc)
set @sqlstr=@sqlstr+('union select * from User where name="'+CONVERT(varchar(100),@userName)+'" and surname="'+convert(varchar(100),@userSurname)+'" ')
print @i
print @sqlstr
set @i=@i+1
end

exec sp_executesql @sqlstr

set   @error   =   @@error
if   @error   <> 0
begin
print   '查询失败'
rollback   tran

end