Thanks Tom. I'll have a play with the various alternatives - and keep the code flexible enough to allow them to be swapped without much fuss.
Alex 2008/5/30 Tom Hughes <[EMAIL PROTECTED]>: > In message <[EMAIL PROTECTED]> > Alex Wilson <[EMAIL PROTECTED]> wrote: > > > Ah. good point - a sensible third way. Apologies for missing it, I'm a > > relative SQL novice. However, if you fetch the tags along with the ways > > using a join, given that there are potentially many tags per way - > couldn't > > you end up with considerable duplication of the way data in the query > > result? I suppose one would have to profile both the join method and my > > local storage method to see which had better memory and time performance. > > You will get some duplication, yes. How much that matters will be > down to profiling as you say. > > The other option is to run two queries in parallel: > > SELECT * > FROM current_ways > WHERE tile IN (...) > AND latitude BETWEEN ... AND ... > AND longitude BETWEEN ... AND ... > ORDER BY id; > > and: > > SELECT cwt.* > FROM current_way_tags cwt > INNER JOIN current_ways cw ON cwt.id = cw.id > WHERE cw.tile IN (...) > AND cw.latitude BETWEEN ... AND ... > AND cw.longitude BETWEEN ... AND ... > ORDER BY cwt.id > > then read both result sets at the same time and match them up. > > Tom > > -- > Tom Hughes ([EMAIL PROTECTED]) > http://www.compton.nu/ >
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