SQL Server 查找不同行之间的 datediff、总和

我正在尝试构建一个查询来分析我们的时间跟踪系统中的数据。每次用户滑入或滑出时，它都会生成一行记录滑入时间以及“在场”或“场外”（进入或退出）。在用户“Joe Bloggs”的情况下，有 4 行，我想将其配对并计算 Joe Bloggs 在网站上花费的总时间。

问题是有些记录不太容易配对。在给出的示例中，第二个用户有两个连续的“开”，我需要找到一种方法来忽略重复的“开”或“关”行。

ID  | Time                    |OnOffSite| UserName   
------------------------------------------------------
123 | 2011-10-25 09:00:00.000 | on      | Bloggs Joe |
124 | 2011-10-25 12:00:00.000 | off     | Bloggs Joe |
125 | 2011-10-25 13:00:00.000 | on      | Bloggs Joe |
126 | 2011-10-25 17:00:00.000 | off     | Bloggs Joe |
127 | 2011-10-25 09:00:00.000 | on      | Jonesy Ian |
128 | 2011-10-25 10:00:00.000 | on      | Jonesy Ian |
129 | 2011-10-25 11:00:00.000 | off     | Jonesy Ian |
130 | 2011-10-25 12:00:00.000 | on      | Jonesy Ian |
131 | 2011-10-25 15:00:00.000 | off     | Jonesy Ian |

我的系统是MS SQL 2005。查询的报告周期是每月。

有人能提出解决方案吗？我的数据已按用户名和时间分组在表中，ID 字段为“身份”。

-- =====================
-- sample data
-- =====================
declare @t table
(
    ID int,
    Time datetime,
    OnOffSite varchar(3),
    UserName varchar(50)
)

insert into @t values(123, '2011-10-25 09:00:00.000', 'on', 'Bloggs Joe')
insert into @t values(124, '2011-10-25 12:00:00.000', 'off', 'Bloggs Joe')
insert into @t values(125, '2011-10-25 13:00:00.000', 'on', 'Bloggs Joe')
insert into @t values(126, '2011-10-25 17:00:00.000', 'off', 'Bloggs Joe')
insert into @t values(127, '2011-10-25 09:00:00.000', 'on', 'Jonesy Ian')
insert into @t values(128, '2011-10-25 10:00:00.000', 'on', 'Jonesy Ian')
insert into @t values(129, '2011-10-25 11:00:00.000', 'off', 'Jonesy Ian')
insert into @t values(130, '2011-10-25 12:00:00.000', 'on', 'Jonesy Ian')
insert into @t values(131, '2011-10-25 15:00:00.000', 'off', 'Jonesy Ian')

-- =====================
-- solution
-- =====================
select
    UserName, timeon, timeoff, diffinhours = DATEDIFF(hh, timeon, timeoff)
from
(
    select
        UserName,
        timeon = max(case when k = 2 and OnOffSite = 'on' then Time end),
        timeoff = max(case when k = 1 and OnOffSite = 'off' then Time end)
    from
    (
        select
            ID,
            UserName,
            OnOffSite,
            Time,
            rn = ROW_NUMBER() over(partition by username order by id)
        from
        (
            select
                ID,
                UserName,
                OnOffSite,
                Time,
                rn2 = case OnOffSite 
                -- '(..order by id)' takes earliest 'on' in the sequence of 'on's
                -- to take the latest use '(...order by id desc)'
                when 'on' then 
                    ROW_NUMBER() over(partition by UserName, OnOffSite, rn1 order by id)
                -- '(... order by id desc)' takes the latest 'off' in the sequence of 'off's
                -- to take the earliest use '(...order by id)'
                when 'off' then
                    ROW_NUMBER() over(partition by UserName, OnOffSite, rn1 order by id desc)
                end,
                rn1
            from
            (
                select
                    *,
                    rn1 = ROW_NUMBER() over(partition by username order by id) +
                        ROW_NUMBER() over(partition by username, onoffsite order by id desc)
                from @t
            ) t
        ) t
        where rn2 = 1
    ) t1
    cross join
    (
        select k = 1 union select k = 2
    ) t2
    group by UserName, rn + k
) t
where timeon is not null or timeoff is not null
order by username