Найти производителей изготавливающие пк но не ноуты. Решение через GROUP BY
SELECT MAKER FROM PRODUCT GROUP BY MAKER HAVING MAX(CASE WHEN TYPE = 'PC' THEN 1 ELSE 0 END) = 1 AND MAX(CASE WHEN TYPE = 'LAPTOP' THEN 1 ELSE 0 END) = 0
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select distinct maker from Product
where maker in (
select distinct maker from Product
where model in (
select model from pc
where code in (Select code from PC
where ram = (select MIN(ram) from pc))
and speed = (select max(speed) from pc
where code in (Select code from PC
where ram = (select MIN(ram) from pc)))
))
and Product.type = 'Printer'