สอบถามเรื่องการใช้ optgroup ที่ใช้ข้อมูลจาก DB ครับ

         <select name="cou_id">
            <optgroup label="หลักสูตร">
                <?PHP
                    $sql = "SELECT * FROM course WHERE cou_type = '0' ORDER BY cou_name ASC";
                    $result = mysql_query($sql);
                    while($show = mysql_fetch_array($result)){
                    if($show1['cou_id'] == $show['cou_id']){ $sel="selected"; }else{$sel=""; }
                ?>
                <option value="<?=$show['cou_id']?>" <?=$sel;?>><?=$show['cou_name']?></option>
                <?PHP } ?>
            </optgroup>
            <optgroup label="สำนักงาน">
                <?PHP
                    $sql = "SELECT * FROM course WHERE cou_type = '1' ORDER BY cou_name ASC";
                    $result = mysql_query($sql);
                    while($show = mysql_fetch_array($result)){
                    if($show1['cou_id'] == $show['cou_id']){ $sel="selected"; }else{$sel=""; }
                ?>
                <option value="<?=$show['cou_id']?>" <?=$sel;?>><?=$show['cou_name']?></option>
            <?PHP } ?>
            </optgroup>
        </select>