PostgreSQL latitude longitude query

Question

i have latitude and longitude columns in location table in PostgreSQL database, and I am trying to execute distance query with a Postg

Answer 1

A more accurate version of @strkol's answer, using the Haversine formula

CREATE OR REPLACE FUNCTION distance(
    lat1 double precision,
    lon1 double precision,
    lat2 double precision,
    lon2 double precision)
  RETURNS double precision AS
$BODY$
DECLARE
    R integer = 6371e3; -- Meters
    rad double precision = 0.01745329252;

    φ1 double precision = lat1 * rad;
    φ2 double precision = lat2 * rad;
    Δφ double precision = (lat2-lat1) * rad;
    Δλ double precision = (lon2-lon1) * rad;

    a double precision = sin(Δφ/2) * sin(Δφ/2) + cos(φ1) * cos(φ2) * sin(Δλ/2) * sin(Δλ/2);
    c double precision = 2 * atan2(sqrt(a), sqrt(1-a));    
BEGIN                                                     
    RETURN R * c;        
END  
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

Input is in degrees (e.g. 52.34273489, 6.23847) and output is in meters.