PHP と MySQL でカンマ区切りのリストからキーワードを分割して保存する方法は?

<code class="php">// Connect to the database
$mysqli = new mysqli($host, $user, $password, $database);

// Initialize variables
$stmt = $mysqli->prepare("SELECT post_id, tags_csv FROM post_tags");
$stmt->execute();
$result = $stmt->get_result();

// Loop through the post tags
while ($row = $result->fetch_assoc()) {
    $post_id = $row['post_id'];
    $tags = explode(',', $row['tags_csv']);

    // Insert unique keywords into the Keywords table
    foreach ($tags as $tag) {
        $stmt = $mysqli->prepare("INSERT IGNORE INTO keywords (name) VALUES (?)");
        $stmt->bind_param("s", $tag);
        $stmt->execute();
    }

    // Get keyword IDs and insert into Post_Keywords table
    foreach ($tags as $tag) {
        $stmt = $mysqli->prepare("SELECT keyword_id FROM keywords WHERE name = ?");
        $stmt->bind_param("s", $tag);
        $stmt->execute();
        $result = $stmt->get_result();
        $keyword_id = $result->fetch_assoc()['keyword_id'];

        $stmt = $mysqli->prepare("INSERT IGNORE INTO post_keywords (post_id, keyword_id) VALUES (?, ?)");
        $stmt->bind_param("ii", $post_id, $keyword_id);
        $stmt->execute();
    }
}</code>