Question

I have to:

Find the makers that sell PCs but not laptops.

This query is not outputting correct result:

SELECT maker, type FROM product
WHERE type = 'PC' AND type <> 'Laptop'

Output from this and correct output:

Result set from this query:

SELECT maker, type FROM product

Table schema:

Even this one is not working:

SELECT maker, type FROM product
WHERE type IN('PC') AND type NOT IN('Laptop')

NOTE – type is added just for clarification

Answer 1

Try:

SELECT maker
FROM product
GROUP BY maker
HAVING SUM(CASE WHEN type = 'PC' THEN 1 ELSE 0 END) > 0
   AND SUM(CASE WHEN type = 'Laptop' THEN 1 ELSE 0 END) = 0