declare @t table 
(UserID varchar(6),
CreatedServer datetime,
LoginClient datetime,
LogoutClient datetime,
Minutes  int
)
insert into @t
select '1785','2011-12-01 08:18:03.490','2011-12-01 08:18:00.683','2011-12-01 15:14:00.683',416 union all
select '1920','2011-12-01 08:23:21.647','2011-12-01 08:23:22.493','2011-12-01 10:50:22.493',147 union all
select '1928','2011-12-01 08:55:23.770','2011-12-01 08:55:38.597','2011-12-01 19:37:38.597',642 union all
select '1914','2011-12-01 11:24:35.753','2011-12-01 11:24:57.620','2011-12-01 13:03:57.620',99 union all
select '1902','2011-12-01 11:39:49.387','2011-12-01 11:40:06.367','2011-12-01 16:22:06.367',282 union all
select '1791','2011-12-01 11:57:18.327','2011-12-01 11:57:24.983','2011-12-01 12:58:24.983',61 union all
select '1939','2011-12-01 16:48:29.563','2011-12-01 16:48:27.397','2011-12-01 20:26:27.397',218 union all
select '1886','2011-12-01 18:09:47.187','2011-12-01 18:09:48.683','2011-12-01 18:24:48.683',15 union all
select '1889','2011-12-01 18:10:02.917','2011-12-01 18:09:59.487','2011-12-01 18:44:59.487',35 union all
select '1886','2011-12-01 18:26:11.113','2011-12-01 18:26:13.430','2011-12-01 18:33:13.430',7 union all
select '1886','2011-12-01 18:32:47.050','2011-12-01 18:32:49.587','2011-12-01 18:55:49.587',23 union all
select '1902','2011-12-02 09:03:14.990','2011-12-02 09:03:09.417','2011-12-02 10:31:09.417',88 union all
select '1940','2011-12-02 09:04:10.117','2011-12-02 09:04:10.740','2011-12-02 09:05:10.740',1 union all
select '1913','2011-12-02 09:04:48.230','2011-12-02 09:04:46.600','2011-12-02 10:17:46.600',73 union all
select '1913','2011-12-02 11:22:40.333','2011-12-02 11:22:38.660','2011-12-02 12:38:38.660',76 union all
select '1920','2011-12-02 12:39:02.877','2011-12-02 12:39:00.803','2011-12-02 14:57:00.803',138 union all
select '1920','2011-12-02 14:56:44.883','2011-12-02 14:56:43.467','2011-12-02 14:58:43.467',2

select * from @t

------解决方案--------------------
SQL code

create function getusercount
(@userID int,@logintime datetime,@logouttime datetime)
returns int
as
begin
    declare @i int 
    select