Martin Martin - 7 months ago 41
SQL Question

MySQL latitude and Longitude table setup

I want to store latitude and longitude values of places in a mysql database table. With the future in mind I will want to be able to find these places within a certain radius of a specific location. Having said that, what datatypes should I store the latitude and longitude values in? Please could you provide me with a create table script for columns like so:

place_id | lat | long


Is there perhaps a column I am missing in the above table that will provide me with additional information that I may not see I need at the current time?

Thanks for any help.

Answer

You should store the points in a singe column of datatype Point which you can index with a SPATIAL index (if your table type is MyISAM):

CREATE SPATIAL INDEX sx_place_location ON place (location)

SELECT  *
FROM    mytable
WHERE   MBRContains
               (
               LineString
                       (
                       Point($x - $radius, $y - $radius),
                       Point($x + $radius, $y + $radius)
                       )
               location
               )
        AND Distance(Point($x, $y), location) <= $radius

This will drastically improve the speed of queries like "find all within a given radius".

Note that it is better to use plain TM metrical coordinates (easting and northing) instead of polar (latitude and longitude). For small radii, they are accurate enough, and the calculations are simplified greatly. If all your points are in one hemishpere and are far from the poles, you can use a single central meridian.

You still can use polar coordinates of course, but the formulae for calculating the MBR and the distance will be more complex.

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