จอย มาครึ่งวันไม่ได้ซะที ชี้แนะหน่อยครับ ลองหลายแบบแต่ยังไมผ่านครับ

select a.topic, a.title, a.datepost, b.username 
from topic as a
left join admin_user as b on a.amd_id = b.amd_id

select count(amd_id) as crp, max(date_reply) as mdr from reply where reply.topic_id=topic.topic_id

select a.topic, a.title, a.datepost, b.username, count(c.amd_id) as crp, max(c.date_reply) as mdr  
from topic as a
left join admin_user as b on a.amd_id = b.amd_id
left join reply as c on c.topic_id=a.topic_id
group by a.topic_id

<?  include("include/connect.php");
					include 'include/paging.inc.php';

					$current_page = 1;
					if(isset($_GET['page'])) 
 					{
				 		 $current_page = $_GET['page'];
 					}
					$rows_per_page = 4;
					$start_row = paging_start_row($current_page, $rows_per_page);

					$sql = "SELECT	SQL_CALC_FOUND_ROWS *,DATE_FORMAT(date_post, '%d-%m-%Y : %H.%i.%s') AS datepost, 

					 		a.topic, a.title, a.datepost, b.username, count(c.amd_id) as crp, max(c.date_reply) as mdr  
							from topic as a
							left join admin_user as b on a.amd_id = b.amd_id
							left join reply as c on c.topic_id=a.topic_id
							group by a.topic_id

							ORDER BY date_post  DESC
					 		LIMIT $start_row, $rows_per_page;";


							
					$result = mysql_query($sql);

					$found_rows = mysql_query("SELECT FOUND_ROWS();");
					$total_rows = mysql_result($found_rows, 0, 0);
					$total_pages = paging_total_pages($total_rows, $rows_per_page);

				?>
				<p class="newtopic"><a href="newtopic.php" target="_blank">ตั้งกระทู้ใหม่</a></p>
	    		<table border="1">
	    			<tr>
	    				<th>หัวข้อ</th>
	    				<th width="150">เริ่มโดย</th>
	    				<th width="40">ตอบ</th>
	    				
	    				<th width="180">ตอบล่าสุด</th>
	    			</tr>

	    			<?
						while($rows = mysql_fetch_array($result))         
						{
					?>

	    			<tr>
		    			<td><a href="Webboard_ListPost_Detail.php?topicid=<?=$rows["topic_id"];?>" target="_blank"><?=$rows["title"];?></a></td>
		    			<td><center><?=$rows["username"];?><br><?=$rows["datepost"];?></center></td>
		    			<td><center><?=$rows["num_reply"];?></center></td>
		    			
		    			<td><?=$rows["date_reply"];?> <br><span>โดย <?=$rows["username"];?></span></td>
		    		</tr>
					<?}?>
					</table>
					<?
						
						echo "<h4  align='center'>หน้า: $current_page / $total_pages <br /></h4>";
						$page_range = 5;
						$qry_string = "";	

						$page_str = paging_pagenum($current_page, $total_pages, $page_range, $qry_string);
						echo "<h5 align='center'>$page_str;</h5>"
					?>

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource

    SELECT a.topic, a.title, a.datepost, b.username, count( c.amd_id ) AS crp, max( c.date_reply ) AS mdr
    FROM topic AS a
    LEFT JOIN admin_user AS b ON a.amd_id = b.amd_id
    LEFT JOIN reply AS c ON c.topic_id = a.topic_id
    GROUP BY a.topic_id
    LIMIT 0 , 30 

select a.topic_id, a.title, a.date_post, b.username, count(c.amd_id) as crp, max(c.date_reply) as mdr 
from topic as a left 
join admin_user as b on a.amd_id = b.amd_id 
left join reply as c on c.topic_id=a.topic_id group by a.topic_id