Question

我的网站上有文章，我希望能够按标签订购。每篇文章都有一些标签相关联。

我使用3个表：

medias （代表文章）

+----+--------+-----+
| id | title  | ... |
+----+--------+-----+
|  1 | hello  | ... |
|  2 | hi     | ... |
+----+--------+-----+

标签

+----+------+-----+
| id | name | ... |
+----+------+-----+
|  1 | red  | ... |
|  2 |square| ... |
+----+------+-----+

medias_tags （为了将标签和媒体链接在一起）

+----+----------+--------+
| id | media_id | tag_id |
+----+----------+--------+
|  1 |        1 |      1 |
|  2 |        1 |      2 |
|  3 |        2 |      2 |
+----+----------+--------+

到目前为止，我正在使用这个MySQL / PHP代码按标签订购文章，这是有效的（我故意删除了分页条件以便更好地理解）：

$ BDD

try{
    $bdd = new PDO('mysql:host=localhost;dbname=DB;charset=utf8', 'username', 'pass');}catch(Exception $e) { die('Erreur : '.$e->getMessage());
}



if(isset($_GET['tag'])){
    $tag_name_1 = htmlspecialchars($_GET['tag']);
    $req_tag = $bdd->prepare('SELECT * FROM tags WHERE name = ?');
    $req_tag->execute(array($tag_name_1));
    $data_tag = $req_tag->fetch();
    $ttag_id = $data_tag['id'];     

    $q = 'SELECT * 
          FROM medias 
          JOIN medias_tags 
          ON medias.id=medias_tags.media_id 
          WHERE medias_tags.tag_id ='.$ttag_id.' 
          ORDER BY date DESC 
          LIMIT '.$start.','.$limit;       
    }

    $req_mda_list = $bdd->query($q);

问题是当我想显示与文章相关的所有标签时。 $ mda_tags_list 为空。

while ($data_mda = $req_mda_list->fetch()){

    $mda_id = $data_mda['id'];
    $mda_title = $data_mda['title'];

    #Get media tags
    $req_mda_tags = $bdd->prepare('SELECT * FROM medias_tags WHERE media_id = ?');
    $req_mda_tags->execute(array($mda_id));      

    $mda_tags_list = null;

    while ($data_mda_tags = $req_mda_tags->fetch()){
        $tag_id = $data_mda_tags['tag_id'];

        $req_tag_name = $bdd->prepare('SELECT * FROM tags WHERE id = ?');
        $req_tag_name->execute(array($tag_id));
        $data_tag_name = $req_tag_name->fetch();

        $mda_tags_list .= '<a href="http://www.website.com/tags/'.$data_tag_name['name'].'">'.$data_tag_name['name'].'</a> ';
}

    echo $mda_title.' - '.$mda_tags_list;

}

我真正得到的是：

Order by tag -> Square

Title1 - Tag :
Title5 - Tag : 
Title6 - Tag :

我想要的是：

Order by tag -> Square

Title1 - Tag : Square, Red, Thank
Title5 - Tag : Yellow, Square, You
Title6 - Tag : Square, Blue, Stackoverflow

Answer 1

要让媒体获取所有标签，您可以使用以下查询：

SELECT medias.id,medias.title,GROUP_CONCAT(tags.name) as tag
FROM medias 
JOIN medias_tags ON medias.id = medias_tags.media_id
JOIN tags ON medias_tags.tag_id = tags.id
GROUP BY medias.id

要获取所有媒体以及标签（如果可用，则为空白），您可以使用以下查询：

SELECT medias.id,medias.title,GROUP_CONCAT(tags.name) as tag
FROM medias 
LEFT JOIN medias_tags ON medias.id = medias_tags.media_id
LEFT JOIN tags ON medias_tags.tag_id = tags.id
GROUP BY medias.id

Answer 2

我所做的是简化你的代码，我把你的SQL减少到一个语句，我添加了一些非常基本的错误检查：

$tagName = htmlspecialchars($_GET['tag']);

$sql = "SELECT 
        medias.*,
        GROUP_CONCAT(tags2.name) AS allTags
    FROM
        medias
        -- Get the media tags
        JOIN medias_tags ON medias.id = medias_tags.media_id
        -- Join on the tags so we can add a where condition
        JOIN tags ON medias_tags.tag_id = tags.id
        -- Rejoin tags again, this won't be used as a condition hence the left
        LEFT JOIN tags AS tags2 ON medias_tags.tag_id = tags2.id
    WHERE
        -- Only get medias where it has a matching tag name
        tag.name = :name
    GROUP BY
        medias.id
    ORDER BY
        date DESC
    LIMIT
        :offset, :limit";

$sth = $bdd->prepare($sql);

// Did it prepare ok?
if (!$sth) {
    echo "\nPDO::errorInfo():\n";
    print_r($dbh->errorInfo());
    exit;
}

$err = $sth->execute(array(':name' => $tagName, ':offset' => $start, ':limit' => $limit));

// Did it execute ok?
if (!$sth) {
    echo "\nPDO::errorInfo():\n";
    print_r($dbh->errorInfo());
    exit;
}

foreach ($sth->fetchAll() as $row) {
    $tags = explode(',', $row['allTags']);

    echo $row['title'] . ' - ';

    foreach ($tags as $tag) {
        echo '<a href="http://www.website.com/tags/' . $tag . '">' . $tag . '</a> ';
    }
}

我的SQL注释可能需要删除，如果您的标记包含逗号，这也无法正常工作。如果需要，您可以指定不同的分隔符以避免这种情况。

基本上，只是减少可能失败的区域并抓住可能的区域。我只是试图按照你的例子输出你的代码看起来像什么，希望这能为你提供一些可以实现目标的东西。

MySQL没有显示数据

2 个答案: