Mysql 带标签的海螺

我通过以下查询选择照片、它们的标签和一些基本用户信息：

SELECT photos.*, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS photo_tags 
    FROM photos 
        INNER JOIN users 
            ON photos.upload_by = users.user_id
        INNER JOIN tags_photos 
            ON tags_photos.photo_id = photos.photo_id
        INNER JOIN tags 
            ON tags.tag_id = tags_photos.tag_id
    WHERE photos.status = '$status' 
        AND photos.photo_id IN (SELECT photos.photo_id 
                                    FROM photos
                                        JOIN tags_photos 
                                            ON photos.photo_id = tags_photos.photo_id
                                        JOIN tags 
                                            ON tags_photos.tag_id = tags.tag_id) 
    GROUP BY photos.photo_id 
    ORDER BY status, upload_date;

它工作得很好，唯一的例外是，如果照片没有标签，它不会返回该照片。我希望它仍然返回照片，即使没有标签

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有人有什么建议吗？

看起来你需要在

标签和
照片之间有一个
右外连接

SELECT photos.*, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS photo_tags FROM photos 
    INNER JOIN users ON photos.upload_by = users.user_id
    RIGHT OUTER JOIN tags_photos ON tags_photos.photo_id = photos.photo_id
    INNER JOIN tags ON tags.tag_id = tags_photos.tag_id
    WHERE photos.status = '$status' AND photos.photo_id IN (
        SELECT photos.photo_id 
        FROM photos
        LEFT OUTER JOIN tags_photos ON photos.photo_id = tags_photos.photo_id
        JOIN tags ON tags_photos.tag_id = tags.tag_id
    ) 
    GROUP BY photos.photo_id ORDER BY status, upload_date;

看起来您需要在
标签\u照片
和
照片

SELECT photos.*, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS photo_tags FROM photos 
    INNER JOIN users ON photos.upload_by = users.user_id
    RIGHT OUTER JOIN tags_photos ON tags_photos.photo_id = photos.photo_id
    INNER JOIN tags ON tags.tag_id = tags_photos.tag_id
    WHERE photos.status = '$status' AND photos.photo_id IN (
        SELECT photos.photo_id 
        FROM photos
        LEFT OUTER JOIN tags_photos ON photos.photo_id = tags_photos.photo_id
        JOIN tags ON tags_photos.tag_id = tags.tag_id
    ) 
    GROUP BY photos.photo_id ORDER BY status, upload_date;

不确定为什么需要WHERE子句中的IN子查询

SELECT photos.*, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS photo_tags 
    FROM photos 
        INNER JOIN users 
            ON photos.upload_by = users.user_id
        LEFT JOIN tags_photos 
            INNER JOIN tags 
                ON tags.tag_id = tags_photos.tag_id
            ON tags_photos.photo_id = photos.photo_id
    WHERE photos.status = '$status' 
    GROUP BY photos.photo_id 
    ORDER BY status, upload_date;

不确定为什么需要WHERE子句中的IN子查询

SELECT photos.*, GROUP_CONCAT(tags.tag SEPARATOR ', ') AS photo_tags 
    FROM photos 
        INNER JOIN users 
            ON photos.upload_by = users.user_id
        LEFT JOIN tags_photos 
            INNER JOIN tags 
                ON tags.tag_id = tags_photos.tag_id
            ON tags_photos.photo_id = photos.photo_id
    WHERE photos.status = '$status' 
    GROUP BY photos.photo_id 
    ORDER BY status, upload_date;

Michael，谢谢你的提示，但不幸的是，这不起作用。@Pete在子查询中添加的另一个
左外部联接可能会有所帮助。请参见上文。Michael，谢谢你的提示，但不幸的是，这不起作用。@Pete在子查询中添加的另一个
左外部联接可能会有所帮助。见上图。@Pete:很高兴能帮忙。请点击旁边的复选标记，将此答案标记为已接受。@Pete:很高兴为您提供帮助。请单击旁边的复选标记，将此答案标记为已接受。