ID 10318. New Products : StrataScratch

# 회사명, net_difference : output 
# 올해 출시 상품 수 - 작년 출시 상품 수
WITH year_cnt AS    (SELECT  company_name, year, count(product_name) as cnt
                    FROM    car_launches
                    GROUP BY company_name,year)

SELECT  y1.company_name, 
        y1.cnt - y2.cnt as total_launch
FROM    year_cnt y1 INNER JOIN year_cnt y2
        ON y1.company_name = y2.company_name AND y1.year = y2.year + 1