admin

根据帖子ID检索标签

sql

我有三个表:postspost_tagstags。一个帖子可以有多个标签,而一个标签可以属于多个帖子。由于这种多对多关系,我做了一张post_tags桌子。它有两个字段:p_idt_id。它们都是帖子表和标签表的外键。现在,当我运行PHP方法以获取最新帖子时,我还想在一个查询中检索属于该帖子的标签。仅供参考,这是这三个表:

帖子

| p_id | c_id | u_id |   title   |     body    |      published      |
----------------------------------------------------------------------
|  1   |  1   |   1  | first post| lorem ipsum | 2012-01-27 18:37:47 |

post_tags

| p_id | t_id |
---------------
|  1   |  3   |

标签

| t_id |     name    |     slug    |
------------------------------------
|  3   | programming | programming |

这是我现在用来获取不带标签的最新帖子的PHP代码:

public function getLatestPosts()
{
    $query = $this->db->query('SELECT title, clean_title, body, published FROM posts ORDER BY published DESC');
    $blogPosts = array();
    foreach ($query->result() as $row)
    {
        $blogPosts[] = array('title' => $row->title,
                             'clean_title' => $row->clean_title,
                             'body' => $row->body,
                             'published' => $row->published);
    }

    return $blogPosts;
}

如何调整查询以获取属于每个帖子的标签的名称和标签?

谢谢你的帮助!


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2021-07-01

共1个答案

admin

隐式联接:

SELECT title, clean_title, body, published, name, slug
FROM posts, posts_tags, tags
WHERE posts.p_id=posts_tags.p_id AND posts_tags.t_id=tags.t_id
ORDER BY published DESC

显式联接:

SELECT title, clean_title, body, published, name, slug
FROM posts
LEFT JOIN posts_tags ON posts.p_id=posts_tags.p_id
LEFT JOIN tags ON posts_tags.t_id=tags.t_id
ORDER BY published DESC

一次看到正确的,标准化的数据库架构令人耳目一新。

2021-07-01