php-mysql: group by gives error

Question

I have messages table with the following columns: id_message_parent,id_user_from,id_user_to,message,read_date,created,status

I need to select the last message for a user grouped by id_message_parent and tried a lot but all query gives white page of death "500 server error" or return the first in order not last like:

    {"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",.....}]}

Here is what I have tried:

$sql="SELECT *, max(id_message) as max_id FROM `messages` WHERE (`id_user_to`='".$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`";

and more.... here is the php function

$result = mysql_query($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

I think you have not written query properly in $sql variable or might be u have an error in PHP code.

Use below query in phpmyadmin i think it will solve your requirement

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`";

Thanks.