-- The city engineer wants to know which building footprints are all inside
-- the first polygon of the lots ST_MultiPolygon.
-- The building_id column uniquely identifies each row of the
-- buildingfootprints table. The lot_id column identifies the building's lot.
-- The footprints column stores the buildings' geometries.

CREATE TABLE buildingfootprints (building_id integer,
                                 lot_id      integer,
                                 footprint   ST_MultiPolygon);

CREATE TABLE lots (lot_id integer,
                   lot    ST_MultiPolygon);

INSERT INTO buildingfootprints VALUES(
   506, 1010,
   ST_MPolyFromText('multipolygon (((7.0 45.0,15.0 45.0,15.0 51.0,18.0 51.0,18.0 54.0,8.0 54.0,8.0 51.0,7.0 51.0,7.0 45.0)))',1000)
);

INSERT INTO buildingfootprints VALUES(
   543, 2930,
   ST_MPolyFromText('multipolygon (((26.0 55.0,38.0 55.0,38.0 48.0,34.0 48.0,34.0 50.0,26.0 50.0,26.0 55.0)))',1000)
);

INSERT INTO buildingfootprints VALUES(
   1208, 203,
   ST_MPolyFromText('multipolygon (((8.0 39.0,12.0 39.0,12.0 33.0,17.0 33.0,17.0 22.0,8.0 22.0,8.0 39.0)))',1000)
);

INSERT INTO buildingfootprints VALUES(
   178, 5192,
   ST_MPolyFromText('multipolygon (((26.0 33.0,38.0 33.0,38.0 24.0,33.0 24.0,33.0 27.0,26.0 27.0,26.0 33.0)))',1000)
);

INSERT INTO lots VALUES(
   1010,
   ST_MPolyFromText('multipolygon (((2 57,21.5 57,21.5 38,2 38,2 57)))',1000)
);

INSERT INTO lots VALUES(
   2930,
   ST_MPolyFromText('multipolygon (((21.5 57,40 57,40 38,21.5 38,21.5 57)))',1000)
);

INSERT INTO lots VALUES(
   203,
   ST_MPolyFromText('multipolygon (((21.5 38,40 38,40 20,21.5 20,21.5 38)))',1000)
);

INSERT INTO lots VALUES(
   5192,
   ST_MPolyFromText('multipolygon (((2 20,2 38,21.5 38,21.5 20,2 20)))',1000)
);


-- The query lists the buildingfootprints' building_id and lot_id
-- for all building footprints that are all within the first lot polygon.
-- The ST_GeometryN function returns a first lot polygon element in the
-- ST_MultiPolygon.

SELECT bf.building_id,bf.lot_id
   FROM buildingfootprints bf,lots
   WHERE ST_Within(footprint,ST_GeometryN(lot,1))
   AND bf.lot_id = lots.lot_id;