我不能为我的生活弄清楚这个sql语句有什么问题,以及为什么它没有产生任何结果.如果我拿出LEFT JOIN是有效的,那么它有什么问题呢？
SELECT b.id,r.avg_rating
FROM items AS b
LEFT JOIN
(
SELECT avg(rating) as avg_rating
FROM ratings
GROUP BY item_id
) AS r
ON b.id = r.item_id
WHERE b.creator = " . $user_id . "
AND b.active = 1
AND b.deleted = 0
ORDER BY b.order ASC,b.added DESC
非常感谢帮助.
