php-mysql：分組依據給出錯誤

Question

我有帶有以下列的消息表： id_message_parent,id_user_from,id_user_to,message,read_date,created,status

我需要為按id_message_parent分組的用戶選擇最后一條消息，並嘗試了很多，但所有查詢都給出了死亡的白頁“ 500服務器錯誤”或按順序返回第一條，而不是最后一條：

    {"messages":[{"id_message":"1","id_message_parent":"1","id_user_from":"1","id_user_to":"2","message":"\u0645\u0631\u062d\u0628\u0627 \u0627\u0646\u0627 \u0645\u0633\u062a\u062e\u062f\u0645 1","read_date":null,"created":"2016-10-17 18:13:39","status":"0"}]}

//while it should be
{"messages":[{"id_message":"2","id_message_parent":"1",.....}]}

這是我嘗試過的：

$sql="SELECT *, max(id_message) as max_id FROM `messages` WHERE (`id_user_to`='".$id_user."' OR `id_user_from`='".$id_user."') and `status`='".$status."' GROUP BY `id_message_parent`";

$sql="select * from `messages` where `id_message` in(SELECT *, max(id_message) as max_id FROM `messages` WHERE (`id_user_to`='".$id_user."' OR `id_user_from`='".$id_user."') and `status`='".$status."' GROUP BY `id_message_parent`) x";

$sql="SELECT * FROM `messages` WHERE `id_message` IN (SELECT MAX(id_message) FROM `messages` WHERE (`id_user_to`='".$id_user."' OR `id_user_from`='".$id_user."') and `status`='".$status."') ORDER BY id DESC";

$sql="SELECT * FROM (SELECT * FROM `messages` WHERE `id_user_to`='".$id_user."' OR `id_user_from`='".$id_user."' ORDER BY id DESC) a GROUP BY IF(`id_user_to` = '".$id_user."', `id_user_from`, `id_user_to`)";

$sql="SELECT `id_message`, `id_message_parent`, `id_user_from`, `id_user_to`, `message`, `read_date`, `created`, `status`, GROUP_CONCAT(`id_message`, ',') FROM `messages` GROUP BY `id_message_parent`";

還有更多...這是PHP函數

$result = mysql_query($sql);    
if (mysql_num_rows($result) > 0){   
$messgs=array();
while ($messgs_info= mysql_fetch_array($result)){   
    $info = new Messages();
    $info->id_message=$messgs_info['id_message'];       
    $info->id_message_parent=$messgs_info['id_message_parent'];     
    $info->id_user_from=$messgs_info['id_user_from'];       
    $info->id_user_to=$messgs_info['id_user_to'];   
    $info->message=$messgs_info['message']; 
    $info->read_date=$messgs_info['read_date']; 
    $info->created=$messgs_info['created']; 
    $info->status=$messgs_info['status'];

    array_push($messgs, $info);
}
    echo json_encode(array('messages' => $messgs));
}

Answer 1

我認為您沒有在$ sql變量中正確編寫查詢，或者您可能在PHP代碼中有錯誤。

在phpmyadmin中使用以下查詢，我認為它將解決您的要求

SELECT msg.* FROM  ( 
    SELECT * FROM message  ORDER BY created DESC)  as msg 
    (msg.`id_user_to`= 2 OR msg.`id_user_from`= 1 ) and msg.`status`= '0'  
    GROUP BY msg.`id_message_parent`";

謝謝。