SELECT filtered.geom FROM (
select * from buildings b
where sdo_FILTER(b.geom,
sdo_geometry( 2003, null, null, sdo_elem_info_array(1,1003,3), sdo_ordinate_array( 50,50, 400, 400) ) ) = 'TRUE'
) as filtered
WHERE sdo_NN( filtered, sdo_geometry(2001, null, sdo_point_type(200,200,null),null,null)...