Hi Tom, Thanks for the help - much appreciated.
Yes I'm using PostGIS, and with a simply join to a relating table I could get access to the geometry for these point positions. Is using the GIST r-tree index faster than using the 2 b-tree indexes on the lat and long values? I guess this is a question for the PostGIS guys and a quick test could tell me anyway! My memory is that the GIST r-tree index is slow for points at the moment, and that a good implementation of a kd-tree index over GIST is required for better speed. Regards, Jeremy Palmer Geodetic Surveyor National Geodetic Office Land Information New Zealand | Toitu te whenua 160 Lambton Quay | Private Box 5501 | Wellington 6145 DDI: 64 (0)4 498 3537 | Fax: 64 (0)4 498 3837 | www.linz.govt.nz -----Original Message----- From: Tom Lane [mailto:t...@sss.pgh.pa.us] Sent: Saturday, 10 July 2010 11:20 a.m. To: Jeremy Palmer Cc: pgsql-performance@postgresql.org Subject: Re: [PERFORM] Index usage with functions in where condition Jeremy Palmer <jpal...@linz.govt.nz> writes: > This is the query that does not use the indexes: > SELECT > coo.nod_id, > 6400000*radians(sqrt((coo.value1 - -41.0618)^2+((coo.value2 - > 175.58461)*cos(radians(-41.0618)))^2)) as distance > FROM > crs_coordinate coo > WHERE > coo.value1 between -41.0618-degrees(1200.0/6400000.0) and > -41.0618+degrees(1200.0/6400000.0) and > coo.value2 between > 175.58461-degrees(1200.0/6400000.0)/(cos(radians(-41.0618))) and > 175.58461+degrees(1200.0/6400000.0)/(cos(radians(-41.0618))); Those expressions yield float8, not numeric, and numeric vs float8 isn't an indexable operator for reasons we needn't get into here. You should probably rethink whether numeric is really the best choice of datatype for your columns, if this is the sort of value you expect to work with --- you're paying a considerable price in speed and space for perhaps-illusory precision gains. But if you insist on using numeric then the solution is to cast the expression results to numeric explicitly. BTW I wonder whether you ought not be looking into postgis rather than rolling-your-own coordinate arithmetic ... regards, tom lane ______________________________________________________________________________________________________ This message contains information, which is confidential and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or i...@linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank you. ______________________________________________________________________________________________________ -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
