如何跳过重复项并进行排序

Question

How do I skip duplicates from a database and sort my latest date? And display a foreach unique id do this..

I'm making a simple chat system, what I'm trying to do is to show every used that has sent a message and skip duplicates user_ids.

Also I'm trying to skip user id #1 because that's a admin.

<?php 

    // Read every user in the database
    $conn = new PDO('mysql:host='. DB_HOST .';dbname='. DB_NAME . ';charset=utf8', DB_USER, DB_PASS);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $sth = $conn->prepare("SELECT DISTINCT user_id FROM live_chat ORDER BY message_date ASC;");
    $sth->execute();
?>
<table cellspacing="0" cellpadding="0" border="0" width="330" class="left">
    <tr>
        <td width="330" valign="top">
            <div class="live_chat_users">
                <?php
                    foreach($sth as $row){
                        if($row['user_id'] == 1){

                        }else{
                            echo $row['user_id']; 
                        }
                    }
                ?>
            </div>
        </td>
    </tr>
</table>

SQLfiddle: http://sqlfiddle.com/#!2/aadcaf

Answer 1

Try something like:

SELECT user_id 
FROM live_chat  
WHERE user_id != 1
GROUP BY user_id
ORDER BY message_date ASC