SELECT MIN(rd_x) AS Links, MIN(rd_y) AS Boven, MAX(rd_x) AS Rechts, MAX(rd_y) AS Onder FROM geo_postalcoords SELECT white_subscriber.city, geo_postalcoords.rd_x, geo_postalcoords.rd_y FROM white_subscriber, geo_postalcoords WHERE white_subscriber.postalcode = geo_postalcoords.postalcode AND city = 'Groningen' GROUP BY white_subscriber.postalcode