SELECT COUNT(`CategoryName`)
FROM `fishing_online_store`.`category`
WHERE `CategoryID` IN
    (SELECT `CategoryID` FROM `fishing_online_store`.`group` WHERE `GroupID` IN
        (SELECT `GroupID` FROM `fishing_online_store`.`product` WHERE `ProductID` IN
            (SELECT `ProductID` FROM `fishing_online_store`.`purchasehistory`
            WHERE `PurchaseDate` > LAST_DAY(DATE_SUB(CURDATE() , INTERVAL 2 MONTH)) + INTERVAL 1 DAY
            AND  `PurchaseDate` < DATE_ADD(LAST_DAY(CURDATE() - INTERVAL 1 MONTH), INTERVAL 1 DAY)
)));

SELECT c.CategoryName AS "Категория", COUNT(ph.ProductID) AS "Количество", AVG(p.ProductPrice) AS "Средняя цена"
FROM category c
INNER JOIN `group` g ON g.CategoryID = c.CategoryID
INNER JOIN `product` p ON p.GroupID = g.GroupID
INNER JOIN `purchasehistory` ph ON ph.ProductID = p.ProductID
                            AND ph.PurchaseDate >= LAST_DAY(CURDATE() - INTERVAL 2 MONTH) + INTERVAL 1 DAY
                            AND ph.PurchaseDate < LAST_DAY(CURDATE() - INTERVAL 1 MONTH) + INTERVAL 1 DAY
GROUP BY c.CategoryName;