Hi Steven, Thanks for the suggestion. I think it would work nicely on a more sophisticated db, but in my limited experience - MySQL is pretty dumb about running subqueries and you can end up with O(n2) run time. So it's better to stay with dumb joins unless OSM moves to something a little more heavyweight!
Alex 2008/5/30 Steven te Brinke <[EMAIL PROTECTED]>: > The second query uses a join only to select the correct values, not > because you really want to join the tables. I think that you can achieve > the same by a query like this: > > SELECT * > FROM current_war_tags > WHERE id IN ( > SELECT * > FROM current_ways > WHERE tile IN (...) > AND latitude BETWEEN ... AND ... > AND longitude BETWEEN ... AND ... > ) > ORDER BY id; > > However, I do not know how the db handles subqueries. Thus, I am not > sure if the performance of this query is better. But it seems to be a > more logical way than using a join. (I am not very sure if using > subqueries works at all, because I know some dbs have problems with that.) > It might be worth trying. > > Steven > > > Tom Hughes schreef: > > 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 > > > > > _______________________________________________ > dev mailing list > [email protected] > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev >
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