ค้นหาจำนวนผลิตภัณฑ์ที่ Sony ไม่ได้ผลิต ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
Find number of products which Sony does not make.It is not neccessary to use all the tables.
 manufacturers:  (code [ VARCHAR ] name [ VARCHAR) ]
SELECT COUNT(DISTINCT name) FROM products WHERE NOT name IN (SELECT T1.name FROM products AS T1 JOIN manufacturers AS T2 ON T1.Manufacturer = T2.code WHERE T2.name = 'Sony')