declare @T table ([user] varchar(6),operate varchar(6),time datetime)
insert into @T
select 'LiMing','Login','2010-10-24 08:03:00' union all
select 'WangYi','Login','2010-10-24 08:14:00' union all
select 'WangYi','Logout','2010-10-24 16:14:00' union all
select 'LiMing','Logout','2010-10-24 16:44:00'

;with maco as(
select [user],
datediff(mi,
max(case operate when 'Login' then [time] else '' end),
max(case operate when 'Logout' then [time] else '' end)
) as mi
from @T group by [user])

select [user],ltrim(mi/60)+'小时'+ltrim(mi%60)+'分' as 时长 from maco
/*
user   时长
------ ------------------------------
LiMing 8小时41分
WangYi 8小时0分
*/

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

DROP TABLE tb0
CREATE TABLE tb0
(
    user1 VARCHAR(10),
    operate VARCHAR(10),
    time DATETIME
)
GO
INSERT INTO tb0
SELECT 'LiMing', 'Login', '2010-10-24 08:03:00' UNION
SELECT 'WangYi', 'Login', '2010-10-24 08:14:00' UNION
SELECT 'WangYi', 'Logout', '2010-10-24 16:14:00' UNION
SELECT 'LiMing', 'Logout', '2010-10-24 16:44:00'


SELECT User1,RIGHT(CONVERT(VARCHAR(100),(MAX(time) - MIN(time)),120),8)
FROM tb0
GROUP BY user1,LEFT(time,10)

User1    (No column name)
LiMing    08:41:00
WangYi    08:00:00