TSQL problem to calculate differences between two dates inside one table

Question

In MSSQL 2008 I have table and data which looks like this

create table #tempData
(user_id int,type varchar(10),ts datetime)

insert into #tempData
select 1,'ENTER','2011-01-30 15:00:00'
union all
select 1,'EXIT','2011-01-31 16:00:00'
union all
select 1,'ENTER','2011-02-1 18:00:00'
union all
select 1,'EXIT','2011-02-10 21:00:00'
union all
select 2,'ENTER','2011-01-10 21:00:00'
union all
select 2,'EXIT','2011-01-12 21:00:00'
union all
select 2,'ENTER','2011-01-13 01:00:00'
union all
select 2,'EXIT','2011-01-13 18:00:00'
--AND SO ON --

Now I trying to make query which is going to tell how long one user was inside according to last exit
something like

user_id,exited,time_in_hours
1,'2011-01-31 16:00:00',25 
1,'2011-02-10 21:00:00',219
2,'2011-01-12 21:00:00',48
2,'2011-01-13 18:00:00',17

Sorry if this BAD or ROUGE question and if this is not proper way to ask a question like this. But I am stacked on this for while.

Answer 1

Assuming that

• same-user sessions do not intersect,

• there cannot be an EXIT record without the corresponding ENTER record,

you could try the following:

WITH ranked AS (
  SELECT
    user_id,
    type,
    ts,
    rn = ROW_NUMBER() OVER (PARTITION BY user_id, type ORDER BY ts)
  FROM #tempData
)
SELECT
  tx.user_id,
  exited = tx.ts,
  hours = DATEDIFF(HOUR, tn.ts, tx.ts)
FROM ranked tn
  INNER JOIN ranked tx ON tn.user_id = tx.user_id AND tn.rn = tx.rn
WHERE tn.type = 'ENTER'
  AND tx.type = 'EXIT'

Answer 2

Using CTE's you can do

with
  exits as ( select [user_id],ts from #tempData where type='EXIT'),
  entries as ( select [user_id],ts from #tempData where type='ENTER'),
  result as (
select 
RANK() over (Partition by a.user_id,b.ts order by a.ts desc) as i,
a.[user_id],b.ts as 'Last Exited',DATEDIFF(hh,a.ts,b.ts) as [hours]
from
    entries a inner join exits b on b.[User_id]=a.[User_id] and a.ts<b.ts
  )

select user_id,[Last Exited],hours from result where i=1

This solution however assumes that there is always an exit record than that record always matches to the immediately preceeding entry record