对连接表有限制？

Question

尝试构建允许多个收件人的线程消息传递模块。为此，我有一个收件人表，每行包含一个 message_id 和收件人 ID。下面我创建了一个用户消息列表。该代码有效，但由于创建连接的方式，如果有多个收件人，我会多次收到相同的消息消息，这使得无法限制唯一消息的数量。

是否可以对消息数量添加限制但仍检索收件人列表，可能在语句中使用另一个选择？

我猜该语句下面的 php 准确地显示了我想要实现的目标。

$query = mysql_query(

    "SELECT
        messages.message_id,
        messages.message_parent_id,
        messages.message_from_id ,
        messages.message_from_email,
        messages.message_subject,
        messages.message_body,
        messages.message_sent_datetime,

        u_from.forename AS from_forename,
        u_from.surname AS from_surname,

        m_recipients.recipient_user_id AS recipient_user_id,

        u_to.forename AS to_forename,
        u_to.surname AS to_surname

    FROM messages

    INNER JOIN users AS u_from ON messages.message_from_id = u_from.user_id
    INNER JOIN message_recipients AS m_recipients ON messages.message_id = m_recipients.recipient_message_id
    INNER JOIN users AS u_to ON m_recipients.recipient_user_id = u_to.user_id

    WHERE m_recipients.recipient_user_id = 1 OR messages.message_from_id = 1

    ORDER BY messages.message_sent_datetime DESC

    ");

$messages = [];

while($row=mysql_fetch_array($query))       {

    if (array_key_exists($row['message_id'], $messages)) {
        $messages[$row['message_id']]['to'][] = $row['to_forename'] . ' ' . $row['to_surname'];
    }
    else {
        $messages[$row['message_id']] = [
            'to'       => [$row['to_forename'] . ' ' . $row['to_surname']],
            'from'     => $row['from_forename'] . ' ' . $row['from_surname'],
            'subject'  => $row['message_subject'],
            'body'     => $row['message_body'],
            'datetime' => $row['message_sent_datetime']
        ];
    }
}

Answer 1

下面将返回消息，其中 from 和 to 名称以逗号分隔。

这样就够了吗？

    SELECT
    messages.message_id, messages.message_parent_id, messages.message_from_id ,
    messages.message_from_email, messages.message_subject, messages.message_body,
    messages.message_sent_datetime,

    GROUP_CONCAT(CONCAT(u_from.forename, ' ', u_from.surname)) as from,
    GROUP_CONCAT(CONCAT(u_to.forename, ' ', u_to.surname)) as to

FROM messages

INNER JOIN users AS u_from ON messages.message_from_id = u_from.user_id
INNER JOIN message_recipients AS m_recipients ON messages.message_id = m_recipients.recipient_message_id
INNER JOIN users AS u_to ON m_recipients.recipient_user_id = u_to.user_id

WHERE m_recipients.recipient_user_id = 1 OR messages.message_from_id = 1
GROUP BY messages.message_id
ORDER BY messages.message_sent_datetime DESC

你可能想玩 GROUP_CONCAT(DISTINCT)