SQL Server find datediff between different rows, sum

Question

I am trying to build a query that analyzes data in our time tracking system. Every time a user swipes in or out, it makes a row recording the swipe time and On or Off site (entr

Answer 1

-- =====================
-- 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