gistfile1.rb

        # Returns the distance SQL using the spherical world formula (Haversine).  The SQL is tuned
        # to the database in use.
        def sphere_distance_sql(origin, units)
          lat = deg2rad(origin.lat)
          lng = deg2rad(origin.lng)
          multiplier = units_sphere_multiplier(units)
          case connection.adapter_name.downcase
          when "mysql"
            sql=<<-SQL_END 
                  (ACOS(least(1,COS(#{lat})*COS(#{lng})*COS(RADIANS(#{qualified_lat_column_name}))*COS(RADIANS(#{qualified_lng_column_name}))+
                  COS(#{lat})*SIN(#{lng})*COS(RADIANS(#{qualified_lat_column_name}))*SIN(RADIANS(#{qualified_lng_column_name}))+
                  SIN(#{lat})*SIN(RADIANS(#{qualified_lat_column_name}))))*#{multiplier})
                  SQL_END
          when "postgresql"
            sql=<<-SQL_END 
                  (ACOS(least(1,COS(#{lat})*COS(#{lng})*COS(RADIANS(#{qualified_lat_column_name}))*COS(RADIANS(#{qualified_lng_column_name}))+
                  COS(#{lat})*SIN(#{lng})*COS(RADIANS(#{qualified_lat_column_name}))*SIN(RADIANS(#{qualified_lng_column_name}))+
                  SIN(#{lat})*SIN(RADIANS(#{qualified_lat_column_name}))))*#{multiplier})
                  SQL_END
          when "oracle"
            radian = PI/180
            sql=<<-SQL_END 
                  (ACOS(least(1,COS(#{lat})*COS(#{lng})*COS(#{qualified_lat_column_name}*#{radian})*COS#{qualified_lng_column_name}*#{radian})+
                  COS(#{lat})*SIN(#{lng})*COS(#{qualified_lat_column_name}*#{radian})*SIN(#{qualified_lng_column_name}*#{radian})+
                  SIN(#{lat})*SIN(#{qualified_lat_column_name}*#{radian})))*#{multiplier})
                  SQL_END
          else
            sql = "unhandled #{connection.adapter_name.downcase} adapter"
          end        
        end
        
        # Returns the distance SQL using the flat-world formula (Phythagorean Theory).  The SQL is tuned
        # to the database in use.
        def flat_distance_sql(origin, units)
          lat_degree_units = units_per_latitude_degree(units)
          lng_degree_units = units_per_longitude_degree(origin.lat, units)
          case connection.adapter_name.downcase
          when "mysql"
            sql=<<-SQL_END
                  SQRT(POW(#{lat_degree_units}*(#{origin.lat}-#{qualified_lat_column_name}),2)+
                  POW(#{lng_degree_units}*(#{origin.lng}-#{qualified_lng_column_name}),2))
                  SQL_END
          when "postgresql"
            sql=<<-SQL_END
                  SQRT(POW(#{lat_degree_units}*(#{origin.lat}-#{qualified_lat_column_name}),2)+
                  POW(#{lng_degree_units}*(#{origin.lng}-#{qualified_lng_column_name}),2))
                  SQL_END
          when "oracle"
            sql=<<-SQL_END
                  SQRT(POWER(#{lat_degree_units}*(#{origin.lat}-#{qualified_lat_column_name}),2)+
                  POWER(#{lng_degree_units}*(#{origin.lng}-#{qualified_lng_column_name}),2))
                  SQL_END
          else
            sql = "unhandled #{connection.adapter_name.downcase} adapter"
          end
        end