Left join - nejde alias

$query = mysql_query("
SELECT a.title AS a_title, b.title AS b_title, a.*
FROM board a LEFT JOIN boardcategory  b ON (a.category1 = b.id)  ORDER BY id DESC");

while ($item = mysql_fetch_row($query)) {
    $return.= "<tr>
    <td>".$item["a_title"]."</td>
    <td>".$item["b_title"]."</td>

</tr>";
}

/* --- Definice tabulky --- */
$output.="<p><a href='index.php?p=board&add'><img src='images/icons/new.png' alt='' class='icon' /> Vytvořit nový záznam</a></p>
<table class='list'>
<form action='' method='post' name='delete' enctype='multipart/form-data'>
<thead>
<tr>
    <td>#</td>
    <td>Datum</td>
    <td>Přidáno</td>
    <td>Sejmuto</td>
    <td>Název dokumentu</td>
    <td>Kategorie č. 1</td>
    <td>Kategorie č. 2</td>
    <td>Soubor</td>
    <td>Autor</td>
    <td>Úprava</td>
    <td><img src='images/icons/note.png' alt='note'class='icon' /></td>
</tr>
</thead>
<tbody>";

/* --- SQL  --- */
$query = DB::query("
SELECT a.title AS a_title, b.title AS b_title, a.*, b.*
FROM `" . _mysql_prefix . "-board` a
LEFT JOIN  `" . _mysql_prefix . "-board-category`
b ON (a.category1 = b.id AND a.category2 = b.id) 
ORDER BY a.id DESC
 " . $paging[1]);
 
 // Někde v $query blbne kód.

echo mysql_error();

while ($item = DB::row($query)) {

// Ceck title_a cat #1
    if ($item["a_title"] = "") {
        $cat_a = "Nevybrána žádná kategorie";
    } else {
        $cat_a = $item["a_title"];
    }
// Ceck title_a cat #2
    if ($item["b_title"] = "") {
        $cat_b = "Nevybrána žádná kategorie";
    } else {
        $cat_b = $item["b_title"];
    }

// Ceck files
    $ext = substr($item['file'], 15, 18);
    if (in_array($ext, array("rar", "zip", "tar", "gz", "tgz", "7z", "cab", "xar", "xla", "777", "alz", "arc", "arj", "bz", "bz2", "bza", "bzip2", "dz", "gza", "gzip", "lzma", "lzs", "lzo", "s7z", "taz", "tbz", "tz", "tzip"))) {
        $icon = "archive";
    } elseif (in_array($ext, array("jpg", "jpeg", "png", "gif", "bmp", "jp2", "tga", "pcx", "tif", "ppf", "pct", "pic", "ai", "ico"))) {
        $icon = "image";
        $image = true;
    } elseif (in_array($ext, array("sql", "php", "php3", "php4", "php5", "phtml", "py", "asp", "cgi", "shtml", "htaccess", "txt", "nfo", "rtf", "html", "htm", "xhtml", "css", "js", "ini", "bat", "inf", "me", "inc", "xml"))) {
        $icon = "editable";
    } elseif (in_array($ext, array("wav", "mp3", "mid", "rmi", "wma", "mpeg", "mpg", "wmv", "3gp", "mp4", "m4a", "xac", "aif", "au", "avi", "voc", "snd", "vox", "ogg", "flac", "mov", "aac", "vob", "amr", "asf", "rm", "ra", "ac3", "swf", "flv"))) {
        $icon = "media";
    } elseif (in_array($ext, array("exe", "com", "bat", "dll"))) {
        $icon = "executable";
    } elseif (in_array($ext, array("sld", "slp", "sle"))) {
        $icon = "sl";
    } else {
        $icon = "other";
    }


// table
    $output.= "<tr>
    <td>" . $item["id"] . "</td> - Zde se vrátí ID z sunlight-board-category místo sunlight-board
    <td>" . _formatTime($item["time"]) . "</td>
    <td><span style='color: green'>" . date('d.m.Y', strtotime($item["start"])) . "</span></td>
    <td><span style='color: red'>" . date('d.m.Y', strtotime($item["down"])) . "</span></td>
    <td>" . $item["title"] . "</td> - Zde se výpíše title z  sunlight-board-category místo sunlight-board
    <td>" . $item["a_title"] . "</td> - Zde se nevýpíše nic, ale potřeboval bych title z sunlight-board-category (podle ID)
    <td>" . $item["b_title"] . "</td> - Zde se nevýpíše nic, ale potřeboval bych title z sunlight-board-category (podle ID)
    <td><img src='images/icons/fman/" . $icon . ".png' alt='file' class='icon' />[ <a href='" . $cesta . "/" . $item["file"] . "'>Zobrazit</a> ]</td>
    <td>" . _linkUser($item['author'], 0, 1, 1) . "</td>
    <td align='right'><a href='index.php?p=board&amp;edit=" . $item["id"] . "'><img src='images/icons/edit.png' alt='' class='icon' /> Upravit</a></td>
    <td align='right'><label><input type='checkbox' name='pole[]' value='" . $item["file"] . "' /> Ke smazání</label></td>
</tr>";
}

/* --- pagging  --- */
$output.=" <tr><td colspan=11><div style='float: left'>" . $paging[0] . "</div><div style='float: right'><img src='images/icons/note.png' alt='note'class='icon' /><strong class='text-red'>POZOR!</strong> Data budou nenávratně smazána!!! <input type='submit' name='delete' value='Smazat'  onclick='return _sysConfirm();' /></div></td></tr>
</tbody></table></form>";

SELECT a.title AS title, b.title AS b_title, a.title AS a_title, a.*, b.* FROM `sunlight-board` a LEFT JOIN `sunlight-board-category` b ON (b.id = a.category1) ORDER BY a.id DESC