
SELECT user_id, product_id
FROM online_sale
GROUP BY user_id , product_id
HAVING COUNT(*) > 1
ORDER BY user_id ASC , product_id DESC;
GROUP BY를 활용해 중복을 처리
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SELECT user_id, product_id
FROM online_sale
GROUP BY user_id , product_id
HAVING COUNT(*) > 1
ORDER BY user_id ASC , product_id DESC;
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