There are two fields in the database table, latitude and longitude. (Other fields too, but they are not important now.)
I have a function, where are three parameters: latitude, longitude and max_distance (km).
Is there any way to construct raw PostgreSQL query that returns only the rows that represent location which is within that max_distance (km) measured from given latitude and longitude?
Example parameters latitude=59.9138699, longitude=10.7522451, max_distance=10
To do this, use postgis.
Postgis has functions such as ST_Distance and ST_PointFromText:
select * from tbl
where ST_Distance(
ST_PointFromText('POINT(' || longitude || ' ' || latitude || ')', 4326),
ST_PointFromText('POINT(10.7522451 59.9138699)', 4326)
) < 10000;
To do this fast, you should use a geometry field and index it.
You should also learn a bit about spatial reference systems and SRID. SRID 4326 denotes the WGS84 coordinate system, commonly in use on the web.
