坚持PHP程序。 需要一些想法

Want to make a php program, where there will be a drop down which will contain some name of brands .. after selecting the " first drop down/ brands" products of the selected brand will show on another drop down.. need help . anyone ?

Use javascript function onchange select element and fetch records according to selected first select element value.

<form name="product" method="post" >
<select id="category" name="category" onChange="relodme()">
    <option value=''></option>
    <?php
    $qry = "select * from category order by name";
    $res = mysql_query($qry) or die ("MYSQL ERROR:".mysql_error());
    while ($arr = mysql_fetch_array($res))
    {
        ?> 
            <option value="<?=$arr['category_id']?>" <? if($_POST['category'] == $arr['category_id']) { ?> selected="selected" <? } ?> ><?=$arr['name']?></option>
        <?
    }

    ?>
</select>

<select id="Type" name="Type"  >
    <option value=''></option>
    <?php
    $qry = "select * from subcategory where category_id = '".$_POST['category']."' order by name";
    $res = mysql_query($qry) or die ("MYSQL ERROR:".mysql_error());
    while ($arr = mysql_fetch_array($res))
    {
        ?> 
            <option value="<?=$arr['sub_category_id']?>" <? if($_POST['Type'] == $arr['sub_category_id']) { ?> selected="selected" <? } ?> ><?=$arr['name']?></option>
        <?
    }

    ?>
</select>
</form>

Javascript function:

function relodme()
{
   document.forms[0].action="test1.php";  //your page name give here....
   document.forms[0].submit();
}

What you looking for is called a dependent select. It have barely nothing to do with php (except populating select options). I've found a demo for your case. You will need to install jquery to implement it in your code.

var $city = $(".city").on('change', function() {
  $city.not(this).get(0).selectedIndex = this.selectedIndex;
});

You need to read about jQuery or CSS.

Look at this example (jQuery): http://dev7studios.com/dropit/

so you have to use ajax to do this

$(document).on("change","first select box",function(){
    var id = $("first select box").val();
    $.ajax({
         url: "path to your file where you should write db code",
         type: "POST",
         dataType: "HTML",
         async: false,
         data: {"id": id},
         success: function(data) {
              $("second select box").html(data);  
           // here directly manipulate the data in controller or get the data in success function and manipulate .                   
      }
  });

})

in the file where you write db code

$a = "";
foreach(rows fro db as $a){
    $a .= "<select value='db id'><?= name ?></select>";
}
echo $a;

we are capturing $a to out normal file add making that as the value for our second select box.

Hope it hlps