LEFT, GROUP BY

SELECT LEFT(PRODUCT_CODE, 2) AS CATEGORY, COUNT(*) AS PRODUCTS
FROM PRODUCT
GROUP BY LEFT(PRODUCT_CODE, 2)
ORDER BY CATEGORY;

  

GROUP BY LEFT(PRODUCT_CODE, 2) 부분은 상품 코드의 앞 2자리를 기준으로 그룹화하는 부분입니다. 

그리고 COUNT(*)은 각 그룹에 속하는 행의 개수를 세는 함수