我有一个查询，可以获取消息系统主页所需的所有信息(包括未读消息计数等)...但它当前检索的是原始 线程消息。我想扩充以下查询以获取每个线程中的最新消息。

这个查询非常接近，但是我平庸的 SQL 技能使我无法总结...

$messages = array();
$unread_messages_total = 0;

$messages_query = "
SELECT m.*
    , COUNT(r.id) AS num_replies
    , MAX(r.datetime) AS reply_datetime
    , (m.archived NOT LIKE '%,".$cms_user['id'].",%') AS message_archive
    , (m.viewed LIKE '%,".$cms_user['id'].",%') AS message_viewed 
    , SUM(r.viewed NOT LIKE '%,".$cms_user['id'].",%') AS unread_replies 
    , CASE
        WHEN MAX(r.datetime) >= m.datetime THEN MAX(r.datetime)
        ELSE m.datetime
        END AS last_datetime
FROM directus_messages AS m
LEFT JOIN directus_messages as r ON m.id = r.reply
WHERE m.active = '1'  
AND (m.to LIKE '%,".$cms_user['id'].",%' OR m.to = 'all' OR m.from = '".$cms_user['id']."') 
GROUP BY m.id
HAVING m.reply = '0' 
ORDER BY last_datetime DESC";

foreach($dbh->query($messages_query) as $row_messages){
    $messages[] = $row_messages;
    $unread_messages_total += (strpos($row_messages['archived'], ','.$cms_user['id'].',') === false && ( (strpos($row_messages['viewed'], ','.$cms_user['id'].',') === false && $row_messages['unread_replies'] == NULL) || ($row_messages['unread_replies']>0 && $row_messages['unread_replies'] != NULL) ) )? 1 : 0;
}

在此先感谢您提供的任何帮助!

编辑:(数据库)

CREATE TABLE `cms_messages` (
  `id` int(10) NOT NULL auto_increment,
  `active` tinyint(1) NOT NULL default '1',
  `subject` varchar(255) NOT NULL default '',
  `message` text NOT NULL,
  `datetime` datetime NOT NULL default '0000-00-00 00:00:00',
  `reply` int(10) NOT NULL default '0',
  `from` int(10) NOT NULL default '0',
  `to` varchar(255) NOT NULL default '',
  `viewed` varchar(255) NOT NULL default ',',
  `archived` varchar(255) NOT NULL default ',',
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

编辑 2:(要求)

• 返回特定 user_id 的所有父消息:$cms_user['id']
• 返回该父消息的回复数:num_replies
• 返回该父消息的未读 回复数:unread_replies
• 返回父消息的日期或其最近的回复:last_datetime
• 返回消息是否在存档中:message_archive
• 返回消息是否被查看:message_viewed
• 按 DESC 日期时间顺序返回所有消息
• 返回最新的消息，来自父级或回复，如果有的话(比如gmail)

最佳答案

如果您只有 2 级消息(即只有父消息和直接答案)，您可以尝试这个查询:

select
    root_message.id,
    root_message.active,
    root_message.subject,
    case
        when max_reply_id.max_id is null then 
            root_message.message
        else
            reply_message.message
    end as message,
    root_message.datetime,
    root_message.reply,
    root_message.from,
    root_message.to,
    root_message.viewed,
    root_message.archived
from
    -- basic data
    cms_messages as root_message
    -- ID of last reply for every root message
    left join (
        select 
            max(id) as max_id, 
            reply as parent_id 
        from 
            cms_messages
        where
            reply <> 0 
        group by 
            reply
    ) as max_reply_id on max_reply_id.parent_id = root_message.id                                              
    left join cms_messages as reply_message on reply_message.id = max_reply_id.max_id
where
    root_message.reply = 0

它使用子查询max_reply_id 作为数据源来选择最新答案的ID。如果它存在(即，如果有答案)，则使用 reply_message.message。如果它不存在(没有找到根消息的答案)，则使用 root_message.message。

您还应该考虑表的结构。例如，如果 reply 包含 NULL(如果它是父消息)或现有消息的 ID，则更有意义。目前，您将其设置为 0(不存在的消息的 ID)，这是错误的。 viewed 和 archived 的类型也很奇怪。

编辑:您还应该避免使用 having 子句。尽可能使用 where。

这是一个应该满足您的要求的新查询。如果它有任何问题(即，如果它返回错误的数据)，请告诉我。

与第一个查询一样，它:

• 使用子查询reply_summary 来累积有关回复的数据(最后回复的 ID、回复数和未读回复数)；
• 将此子查询连接到基表；
• 根据 reply_summary.max_reply_id 将 cms_messages 作为 reply_message 加入子查询，以获取有关最后回复(消息、日期时间)的数据。

我已经简化了您确定 last_datetime 的方式 - 现在需要最后回复的时间(如果有任何回复)或原始帖子的时间(当没有找到回复时)。

我没有通过 from 和 to 字段过滤回复。如果有必要，应该更新reply_summary子查询的where子句。

select
    parent_message.id,
    parent_message.subject,
    parent_message.message,
    parent_message.from,
    parent_message.to,
    coalesce(reply_summary.num_replies, 0) as num_replies,
    last_reply_message.datetime as reply_datetime,
    (parent_message.archived NOT LIKE '%,{$cms_user['id']},%') AS message_archive,
    (parent_message.viewed   LIKE     '%,{$cms_user['id']},%') AS message_viewed,
    reply_summary.unread_replies,
    coalesce(last_reply_message.message, parent_message.message) as last_message,
    coalesce(last_reply_message.datetime, parent_message.datetime) as last_datetime
from
    cms_messages as parent_message
    left join (
        select
            reply as parent_id,
            max(id) as last_reply_id,
            count(*) as num_replies,
            sum(viewed not like '%,{$cms_user['id']},%') as unread_replies
        from
            cms_messages
        where
            reply <> 0 and
            active = 1
        group by
            reply
    ) as reply_summary on reply_summary.parent_id = parent_message.id
    left join cms_messages as last_reply_message on last_reply_message.id = reply_summary.last_reply_id
where
    parent_message.reply = 0 and
    parent_message.active = 1 and
    (parent_message.to like '%,{$cms_user['id']},%' or parent_message.to = 'all' or parent_message.from = '{$cms_user['id']}')
order by
    last_datetime desc;

关于php - 获取线程中的最新消息，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/6261062/