Does anyone know how to organize topics by last post?

Like if Topic 1 has post number 5, put it before topic 2, which has post number 4 as the last post.

How would I do that?

<?php

if ($usable != true) {header('location: ./index.php');}else
define('THIS_SCRIPT', 'threads');

function sortThreadsByLatestPost($theBoardId)
{
    $postsQuery = mysql_query("SELECT * FROM `posts` WHERE `forum` = '$theBoardId' ORDER BY `id` DESC");

    $threadsArray = array();

    while( $postsArray = mysql_fetch_assoc($postsQuery) )
    {
        if( !in_array($postsArray['topic'], $threadsArray) )
        {
            $threadsArray[] = $postsArray['topic'];
        }
    }
    return $threadsArray;
}

$threadsIdArray =  sortThreadsByLatestPost($getforum);


$threadsToDisplay = 15;

$rowsQuery = mysql_query("SELECT * FROM `topics` WHERE `forum` = '$getforum'");
$totalrows = mysql_num_rows($rowsQuery);

$totalpages = $totalrows / $threadsToDisplay;
$totalpages = ceil($totalpages);


$page = (int)$_GET['page'];

if( $totalpages == 0 )
{
	$totalpages = 1;
}
if( $page == 0 )
{
	$page++;	
}

$x = $threadsToDisplay * ($page - 1);
$y = $threadsToDisplay * $page;

if( $y > count($threadsIdArray) )
{
	$y = count($threadsIdArray);
}

if ( mysql_num_rows(mysql_query("SELECT * FROM `forums` WHERE id = '$getforum'")) > 0 )
{
	$category1f = mysql_query("SELECT * FROM `forums` WHERE `id` = '$getforum'");
	if (!$category1f)
	{
		$main .=  'Could not run query: ' . mysql_error();
		exit;
	}
}
else
{
	$main .=  'Not found';
	exit;
}


$forumArray = mysql_fetch_assoc($category1f);

$main .=  "
<div class=\"postbutton\">

";

$nextpage = $page + 1;
$prevpage = $page - 1;

$main .=  "<span>";
;if (empty($_SESSION[username])){$main .= '<a href="./index.php?page=login">Login to Post</a>';}
else{if($urlrewrite2 == true){$main .= "<a href='/forums/newtopic/$getforum.html'>Post New Topic</a>";}
else{$main .= '<a href="./index.php?page=newtopic&f=' . $getforum . '">Post New Topic</a>';}}$main .= "
</span>
	";
$main .=  "

		Page $page of $totalpages ";

if( $prevpage != 0  )
{
	$main .=  " <a href=\"?forum=$getforum&amp;page=1\">First page</a> <a href=\"?forum=$getforum&amp;page=". $prevpage ."\">Previous page</a> ";	
}

if( $nextpage <= $totalpages )
{
	$main .=  " <a href=\"?forum=$getforum&amp;page=". $nextpage ."\">Next page</a> <a href=\"?forum=$getforum&amp;page=". $totalpages ."\">Last page</a>";	
}
$main .= "</div>";
/*	
if( empty($_SESSION['username']) )
{
	$main .=  "<a href='/accounts/login.php'>Login to Post</a>";
}
else
{
	if($urlrewrite2 == true)
	{
		$main .=  "<a href='/forums/newtopic/$getforum.html'>Post New Topic</a>";
	}
	else
	{
		$main .=  "<a href='/forums/newtopic.php?forum=$getforum'>Post New Topic</a>";
	}
}*/

$main .= '


<div class="multicode">
<div class="thead"><div class="thead_l"><div class="thead_r"><p>' . $title . '<span>Viewing Threads</span></p></div></div></div>
<div class="tborder">
 <div class="fsection" style="background: #FFFFFF;border-bottom: 1px solid #677ea8;">
<div style="float:right;color: #555555;margin-right: 7%;text-align:right;"><p>
Last Post
</p>
</div>

<div class="col1" style="background:none;width: 60%"><p>
Topic
</p>
</div>

 <div class="col2" style="background:none;width: 100px;text-align:center;"><p>
 Statistics
 </p>
 </div>
</div>
';

    $threadQuery2 = mysql_query("SELECT * FROM `topics` WHERE `forum` = '".$getforum ."'");
    $threadArray2 =  mysql_num_rows($threadQuery2); 

if($threadArray2 < 1){$main .= '<tr><td class="t1" colspan="5"><p style="text-align:center;">There are currently no topics in this forum.</p></td></tr>';}
while( $x < $y )
{
    $threadQuery = mysql_query("SELECT * FROM `topics` WHERE `id` = '".$threadsIdArray[$x] ."'");
    $threadArray = mysql_fetch_assoc($threadQuery);

    $postQuery = mysql_query("SELECT * FROM `posts` WHERE `topic` = '{$threadArray['id']}' ORDER BY `id` DESC LIMIT 1");
    $postArray = mysql_fetch_assoc($postQuery);
	
	$urlsubject=str_replace(" ", "-", $threadArray['subject']); 
	$urlsubject = ereg_replace("[^A-Za-z0-9-]", "", $urlsubject);
	
   $numpostsQuery = mysql_query("SELECT id FROM `posts` WHERE `topic` = '{$threadArray['id']}'");
   $numposts = mysql_num_rows($numpostsQuery); 
   
   $userinfoQuery = mysql_query("SELECT * FROM `members` WHERE `mid` = '{$threadArray['membernumber']}'");
   $userinfoArray = mysql_fetch_array($userinfoQuery);
   
   $userinfo2Query = mysql_query("SELECT * FROM `members` WHERE `mid` = '{$postArray['membernumber']}'");
   $userinfo2Array = mysql_fetch_array($userinfo2Query);
   
   $threadArray['time'] = date("F d, Y", $threadArray['time']);
   $postArray['time'] = date("F d, Y", $postArray['time']);

    $main .=  '
	
	 <div class="fsection" style="background: #f0f4f8;">
	 
<div style="float:right;color: #555555;margin-right: 7%;overflow:hidden;width: 200px;"><p>
' . $postArray['time'] . '<br /><a href="./index.php?topic=' . $threadsIdArray[$x] . '&page=last&' . $urlsubject . '.html#' . $postArray['id'] . '">' . $threadArray['subject'] . '</a><br />By <a href="?id=' . $postArray['membernumber'] . '">' . $userinfo2Array['username'] . '</a>
 
 </p>
 </div>
	 
 <div class="col1" style="width: 60%"><p>
<a href="./index.php?topic=' . $threadArray['id'] . '&page=1&' . $urlsubject . '.html"><b>' . $threadArray['subject'] . '</b></a><span style="font-size: 11px;display:block;">
Topic Starter: <a href="./index.php?member=' . $threadArray['membernumber'] . '">' . $userinfoArray['username'] . '</a></span></p>
</div>


 <div class="col2" style="width: 100px"><p>
<b style="text-align:center;display:block;">' . $threadArray['time'] . '</b>
<span style="font-size: 11px;text-align:center;">Posts:  ' . $numposts . '</span>
</p>
</div>





</div>
<div style="background: #CCCCCC;height: 1px;"></div>

';
    $x++;
}
	
$main .=  "
</div></div>
";
$main .=  "
<div class=\"postbutton\">

";

$nextpage = $page + 1;
$prevpage = $page - 1;


$main .=  "<span>";
;if (empty($_SESSION[username])){$main .= '<a href="./index.php?page=login">Login to Post</a>';}
else{if($urlrewrite2 == true){$main .= "<a class=\"postbutton\" href='/forums/newtopic/$getforum.html'>Post New Topic</a>";}
else{$main .= '<a href="./index.php?page=newtopic&f=' . $getforum . '">Post New Topic</a>';}}$main .= "
</span>




";

$main .=  "

		Page $page of $totalpages ";

if( $prevpage != 0  )
{
	$main .=  " <a href=\"?forum=$getforum&amp;page=1\">First page</a> <a href=\"?forum=$getforum&amp;page=". $prevpage ."\">Previous page</a> ";	
}

if( $nextpage <= $totalpages )
{
	$main .=  " <a href=\"?forum=$getforum&amp;page=". $nextpage ."\">Next page</a> <a href=\"?forum=$getforum&amp;page=". $totalpages ."\">Last page</a>";	
}

$main .=  "</div>";

?>

Code (markup):

A friend made that script for me, but for some reason it doesn't work anymore, and it orders by latest topic rather than the post.

 

Use datetime fields instead of id or posts count.

Regards

 

NEVERMIND, I figured out the problem, it was a problem with the forum column.