I need help with a architectural problem that im working with. The user enters a position and a radius (e.g. distance). The software searches in a (giant = couple of 100k posts) database table for posts where the users location and the “posts” distance to each other is less than the entered distance.
It’s kind of hard for me to explain, but imagine a table with two posts, point a and point c, point U is the user location. The user has entered a position and a radius, and the position and radius for a and c is predefined (stored in a database).
In this case i would only be interested in the point A, because the two areas intersect with each other. How should i transform this into doing in a database with a couple of hundred thousand posts in an effective way? In the database i shall store longitude,latitude and radius.
Depends on which database server you’re using, but look into the GIS capabilities that might be included. For example, MS SQL Server 2008 has a built-in geometry type, and PostgreSQL has PostGIS. Oracle has something like this too. Anyhow – these native GIS formats come with spacial querying functions that do the sort of thing you’re talking about – searching for matches within given distances, etc… It is pretty simple to accomplish once to switch to the proper datatype.
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Since you’re using SQL 2008, and your data is lat/long, I suggest the “geography” rather than the “geometry” datatype. Take a look here: http://msdn.microsoft.com/en-us/library/cc280766.aspx