$query = "SELECT A.*
FROM A
LEFT JOIN B
ON A.id = B.id_catalog
ORDER BY A.catalog ASC";
$result = mysql_query($query);
$select = '<select name="category">';
while ($row = mysql_fetch_assoc($result)) {
$select .= '<option value="'.$row['id'].'">'. $row['catalog'] .'</option>';
}
$select .= '</select>';
echo $select;