Datediff between two tables - sql

Question

I have those two tables
1-Add to queue table
TransID , ADD date
10 , 10/10/2012
11 , 14/10/2012
11 , 18/11/2012
11 , 25/12/2012
12 , 1/1/2013
2-Removed from queue table
TransID , Removed Date
10 , 15/1/2013
11 , 12/12/2012
11 , 13/1/2013
11 , 20/1/2013
The TansID is the key between the two tables , and I can't modify those tables, what I want is to query the amount of time each transaction spent in the queue
It's easy when there is one item in each table , but when the item get queued more than once how do I calculate that?

Answer 1

Assuming the order TransIDs are entered into the Add table is the same order they are removed, you can use the following:
WITH OrderedAdds AS
( SELECT TransID,
AddDate,
[RowNumber] = ROW_NUMBER() OVER(PARTITION BY TransID ORDER BY AddDate)
FROM AddTable
), OrderedRemoves AS
( SELECT TransID,
RemovedDate,
[RowNumber] = ROW_NUMBER() OVER(PARTITION BY TransID ORDER BY RemovedDate)
FROM RemoveTable
)
SELECT OrderedAdds.TransID,
OrderedAdds.AddDate,
OrderedRemoves.RemovedDate,
[DaysInQueue] = DATEDIFF(DAY, OrderedAdds.AddDate, ISNULL(OrderedRemoves.RemovedDate, CURRENT_TIMESTAMP))
FROM OrderedAdds
LEFT JOIN OrderedRemoves
ON OrderedAdds.TransID = OrderedRemoves.TransID
AND OrderedAdds.RowNumber = OrderedRemoves.RowNumber;
The key part is that each record gets a rownumber based on the transaction id and the date it was entered, you can then join on both rownumber and transID to stop any cross joining.
Example on SQL Fiddle

Answer 2

DISCLAIMER: There is probably problem with this, but i hope to send you in one possible direction. Make sure to expect problems.
You can try in the following direction (which might work in some way depending on your system, version, etc) :
SELECT transId, (sum(add_date_sum) - sum(remove_date_sum)) / (1000*60*60*24)
FROM
(
SELECT transId, (SUM(UNIX_TIMESTAMP(add_date)) as add_date_sum, 0 as remove_date_sum
FROM add_to_queue
GROUP BY transId
UNION ALL
SELECT transId, 0 as add_date_sum, (SUM(UNIX_TIMESTAMP(remove_date)) as remove_date_sum
FROM remove_from_queue
GROUP BY transId
)
GROUP BY transId;
A bit of explanation: as far as I know, you cannot sum dates, but you can convert them to some sort of timestamps. Check if UNIX_TIMESTAMPS works for you, or figure out something else. Then you can sum in each table, create union by conveniently leaving the other one as zeto and then subtracting the union query.
As for that devision in the end of first SELECT, UNIT_TIMESTAMP throws out miliseconds, you devide to get days - or whatever it is that you want.
This all said - I would probably solve this using a stored procedure or some client script. SQL is not a weapon for every battle. Making two separate queries can be much simpler.

Answer 3

Answer 2: after your comments. (As a side note, some of your dates 15/1/2013,13/1/2013 do not represent proper date formats )
select transId, sum(numberOfDays) totalQueueTime
from (
select a.transId,
datediff(day,a.addDate,isnull(r.removeDate,a.addDate)) numberOfDays
from AddTable a left join RemoveTable r on a.transId = r.transId
order by a.transId, a.addDate, r.removeDate
) X
group by transId
Answer 1: before your comments
Assuming that there won't be a new record added unless it is being removed. Also note following query will bring numberOfDays as zero for unremoved records;
select a.transId, a.addDate, r.removeDate,
datediff(day,a.addDate,isnull(r.removeDate,a.addDate)) numberOfDays
from AddTable a left join RemoveTable r on a.transId = r.transId
order by a.transId, a.addDate, r.removeDate