[Programmers] ROOT 아이템 구하기

문제 링크

정답

-- ITEM_INFO: ITEM_ID, ITEM_NAME, RARITY, PRICE
-- ITEM_TREE: ITEM_ID, PARENT_ITEM_ID

SELECT INFO.ITEM_ID, INFO.ITEM_NAME
FROM ITEM_INFO AS INFO
JOIN ITEM_TREE AS TREE ON INFO.ITEM_ID = TREE.ITEM_ID
WHERE TREE.PARENT_ITEM_ID IS NULL

✅ Point

• TABLE JOIN 후, TREE의 PARENT_ITEM_ID가 가 NULL인 row만 count