booktown=# SELECT isbn, cost, retail FROM stock
booktown-# WHERE (isbn, stock)
booktown-# IN (SELECT isbn, 0 FROM editions
booktown(# WHERE type = 'p');
isbn | cost | retail
0394800753 | 16.00 | 16.95
0394900014 | 23.00 | 23.95
0451457994 | 17.00 | 22.95
(3 rows)