–Find all PC’s makers which doesn’t produce laptops
1. SELECT DISTINCT maker
FROM product WHERE
maker NOT IN (SELECT maker FROM product WHERE type =
FROM product WHERE
maker NOT IN (SELECT maker FROM product WHERE type =
‘LAPTOP’)
AND type = ‘PC’
AND type = ‘PC’
2. SELECT DISTINCT p1.maker
FROM product AS p1 LEFT OUTER JOIN
product AS p2 ON p1.maker = p2.maker AND p2.type =
FROM product AS p1 LEFT OUTER JOIN
product AS p2 ON p1.maker = p2.maker AND p2.type =
‘Laptop’
WHERE (p1.type = ‘PC’) AND (p2.maker IS NULL)
WHERE (p1.type = ‘PC’) AND (p2.maker IS NULL)