Question

我有以下查询来选择照片，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;

效果很好，唯一的例外是如果照片没有标签，则不会返回该照片。即使没有标签，我仍然希望它仍然可以返回照片。

有人有任何建议吗？

Answer 1

不确定为什么在WHERE子句中需要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;

Answer 2

您似乎需要RIGHT OUTER JOIN和tags_photos

之间的photos

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;

带标签的CONCAT

2 个答案: