Question

我从数据库中获取标签，并且想要对结果顶部的表tag_posts中具有匹配项的标签进行排序。它接近正常工作，但是由于c_p_id的分组，我得到了重复。但是，如果我按顺序从组中删除c_p_id，有时会提取错误的行。使用某些IF EXIST选项是否更有意义？

我希望这样列出标签：

TAG B
TAG A
TAG C

如果TAG-B在tag_posts中有匹配项。

SELECT c_p_id, t_id, t_title
FROM tags
LEFT JOIN projects
ON p_id = " . $p_id . "
LEFT JOIN tag_posts
ON tp_t_id = t_id
LEFT JOIN cats
ON c_id = tp_c_id
AND c_p_id = p_id
GROUP BY t_id, c_p_id
ORDER BY c_p_id DESC, t_title ASC

//编辑。我想出了一种解决方案，可以满足我的要求：

SELECT t_id, t_title, 
    (SELECT 1 FROM tag_posts
        INNER JOIN cats
            ON c_id = tp_c_id
        INNER JOIN projects
            ON p_id = c_p_id
        WHERE tp_t_id = t_id
            AND p_id = " . $p_id . "
        LIMIT 1) used
FROM tags
ORDER BY used DESC, t_title ASC

Answer 1

解决方案：

SELECT t_id, t_title, 
    (SELECT 1 FROM tag_posts
        INNER JOIN cats
            ON c_id = tp_c_id
        INNER JOIN projects
            ON p_id = c_p_id
        WHERE tp_t_id = t_id
            AND p_id = " . $p_id . "
        LIMIT 1) used
FROM tags
ORDER BY used DESC, t_title ASC

订购匹配项位于顶部的标签

1 个答案: