Calculate stay duration in Answers

Question

Dear Reader,
I trying to solve the following problem and am blocked:
We have a set of objects (1,2,3,...) and a set of knot (A,B,C,...). Each object is going from one knot A to knot D, then staying at knot D for a time period and is going to knot K (A,D and K stay for a random path between knots).
My database has the following structure:
TableA:
-object_ID
TableB:
- departure knot
- departure time at departure knot
- Arrival knot
- Arrival time at arrival knot
(TableA and TableB are connected through a join...)
Now I want to query my database for a certain datetime in order to know which object is at which place and for which duration (total duration, or duration left, or since when). My problem lies in the calculation of the duration. How can I realize the query for a datetime with object_A AND arrival_time in knot_K < departure_time in knot_K?
Any help is greatly appreciated
Evgeny

Answer 1

@john
I don't think that a CONNECT BY PRIOR will resolve the problem because in this kind of statement you can't use the data from the parent in the child row (may be they have made improvement ?). And in this way, you can do the comparison arrival, departure because arrival will be on the parent row while departure will be on the child row. No ?
@evgeny
I think that you have a problem in your model. You would never ask this question, if you had as table B :
- object_ID
- knot
- Arrival time at knot
- departure time at knot
And as said john, you just need to create a table of type view in the physical layer with a self join as :
select
arrival.object_ID,
arrival.Arrival knot
arrival.Arrival time at arrival knot
departure.departure time at departure knot
from
tableB arrival,
tableB departure
where
arrival.Arrival knot = departure.departure knot (+)This view will then replace your tableB and you can answer all your questions.
Cheers
Nico
Edited by: gerardnico on Jul 16, 2009 9:03 PM replace say by said