my %SQL = (
    order_by_date => 'select image_name from image
                      where house_id in (
                        select kitchen_id, bathroom_id
                        from house where house_id=?
                      )
                      order by image_date',

    kitchen_first => 'select image_name from image
                      where image_id =
                      (  select kitchen_id, bathroom_id
                         from house where house_id = ? )',

    bathroom_first => 'select image_name from image
                      where image_id =
                      (  select bathroom_id, kitchen_id
                         from house where house_id = ? )',
);

....
$sth = $dbh->prepare( $SQL{order_by_date} );
....
$sth = $dbh->prepare( $SQL{kitchen_first} );
....