Volanie stranky pre update

<form action="cos_den_zapis.php" method="post">
    <input type=hidden name=datum_vykonu value="<?=$datum_vykonu?>">
    <input type=hidden name=sala_cislo value="<?=$sala_cislo?>">
    <input type=hidden name=epiz value="<?=$row["epiz"]?>">
    <select name="instrumentar" class="instrumentar" onChange="this.form.submit();">
        <option selected="selected">--Inštrumentár--</option>
        <?php

        $sql=mysql_query("select * from instrumentar where ('$datum_vykonu' between zacplatnosti and konplatnosti) order by instrumentar ASC");
        
            while($rowi=mysql_fetch_array($sql))
            {
    
            
            echo '<option value="'.$rowi['id'].'"'.($rowi['id']==$row['instrumentar']?" selected":"").'>'.$rowi['instrumentar'].'</option>';

            }
     ?>
    </select>
    </form>