Aquí les paso el código:
Código PHP:
<?
include ("../db_config.php");
$id_marca = $_GET["id_marca"];
?>
<html>
<head>
<title>
FAQ-1: Selects
</title>
<script language="JavaScript">
function addOpt(oCntrl, iPos, sTxt, sVal){
var selOpcion=new Option(sTxt, sVal);
eval(oCntrl.options[iPos]=selOpcion);
}
function cambia(oCntrl){
while (oCntrl.length) oCntrl.remove(0);
<?
$getModelos = hyt_query("SELECT * FROM modelos WHERE id_marca = '$id_marca'");
while ($rsModelos = hyt_fetch_array($getModelos)){ ?>
addOpt(oCntrl, <?=$rsModelos['id'];?>, <?=$rsMarcas['nombre'];?>, <?=$rsModelos['id'];?>);
<? } ?>
}
</script>
</head>
<body>
<form name="frm">
<table border="0">
<tr>
<td>Marca</td>
<td>
<select name="marca" onchange="cambia(document.frm.modelo)">
<?
$getMarcas = hyt_query("SELECT * FROM marcas");
while ($rsMarcas = hyt_fetch_array($getMarcas)){
if ($id_marca==""){ $id_marca = $rsMarcas['id']; }
?>
<option value="<?=$rsMarcas['id'];?>"><?=$rsMarcas['nombre'];?></option>
<? } ?>
</select>
</td>
<td>
</td>
<td>
Modelo</td>
<td>
<select name="modelo">
<?
$getModelos = hyt_query("SELECT * FROM modelos WHERE id_marca = '$id_marca'");
while ($rsModelos = hyt_fetch_array($getModelos)){
?>
<option value="<?=$rsModelos['id'];?>"><?=$rsModelos['nombre'];?></option>
<? } ?>
</select>
</td>
</tr>
</table>
</form>
</body>
</html>
Gracias!