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好的,我有一個收視表。爲每個留下評分的用戶創建一個新行。我試圖做的是創建一個查詢,該查詢將返回現在和7天前存在的每個特定行的評級值。mysql加入虛擬表
廣義的觀點是,我想計算總平均評分與7天前總平均評分的差異。
我有這個,我認爲是正確的路走下來,但我得到
Unknown column 'start_ratings.menu_item_id' in 'on clause'
SELECT *
FROM ratings end_ratings
JOIN (
SELECT menu_item_id as end_menu_item_id, AVG(value) AS end_rating
FROM ratings
WHERE
created_at > current_date - 7
AND menu_item_id IS NOT NULL
AND location_id IS NOT NULL
GROUP BY menu_item_id
) start_ratings ON (end_ratings.menu_item_id = start_ratings.menu_item_id)
WHERE menu_item_id IS NOT NULL
AND location_id IS NOT NULL;
非常感謝,解決了這個問題,我明白了。 – hcker2000