[LeetCode] 1158. Market Analysis I

 

 

[문제]

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[MySQL]

SELECT u.user_id AS buyer_id
     , u.join_date
     , SUM(CASE WHEN order_date BETWEEN '2019-01-01' AND '2019-12-31'
                  THEN 1
                  ELSE 0
            END) AS orders_in_2019
FROM Users AS u
    LEFT JOIN Orders AS o ON u.user_id = o.buyer_id
GROUP BY u.user_id