# Dbase query performance vs. iterating over large result arra **URL:** \ **Category:** Rails\ **Created:** [July 24, 2007, 11:33pm UTC](https://www.ruby-forum.com/t/dbase-query-performance-vs-iterating-over-large-result-arra/110291 "2007-07-24T23:33:00Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Astorian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ad7895/32.png) [@Astorian](https://www.ruby-forum.com/u/Astorian)\ **Post date:** [July 24, 2007, 11:33pm UTC](https://www.ruby-forum.com/t/dbase-query-performance-vs-iterating-over-large-result-arra/110291/1 "2007-07-24T23:33:00Z")
Hello Folks. Please excuse my beginner’s ignorance … My question regards database query performance vs. iterating over nested results in an array. In the example below, a Project has many Tasks. Tasks have a due date. When I display Projects, I would like to also display the cumulative delay for all open Project Tasks based on their due date, and today’s date. Something like … Project | Delay XYZ | 5 days (4 tasks late, 1.25 day average delay) … 100 records As I learn RoR, I’ve discovered a couple ways I can do this. I can perform the calculations in a single query. I can use the :include option to build an array with nested children, and iterate over each Project’s Tasks with something like parent.child.each.do. Or, finally, I can issue 100 queries to the database, once for each record. Each has advantages, but which is the most commonly accepted method in the RoR community? Thanks in advance John ---
**Author:** ![Astorian](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ad7895/32.png) [@Astorian](https://www.ruby-forum.com/u/Astorian)\ **Post date:** [July 25, 2007, 9:28am UTC](https://www.ruby-forum.com/t/dbase-query-performance-vs-iterating-over-large-result-arra/110291/2 "2007-07-25T09:28:00Z")
Astorian wrote: > Project | Delay > XYZ | 5 days (4 tasks late, 1.25 day average delay) > … 100 records > > As I learn RoR, I’ve discovered a couple ways I can do this. I can > perform the calculations in a single query. I can use the :include > option to build an array with nested children, and iterate over each > Project’s Tasks with something like parent.child.each.do. Or, finally, > I can issue 100 queries to the database, once for each record. Each > has advantages, but which is the most commonly accepted method in the > RoR community? Doing 100 queries to the database sounds like a bad idea. There’s no reason not to use :include in the example given. Try doing it both ways and see the difference in execution time for yourself. – Cheers, - Jacob A.