selected item from combo / drop down to populate text boxes on the same page

Hi experts,

I have a table of postcodes and I am wanting to get the user to select the city, state postcode from a combo box (displayed like city, state, postcode) and have it populate the next two text fields of "State" and "Postcode". I am looking for something like an onchange function to fill the boxes.

The postcode data comes from tblPostcode

Thanks for your help.

the code is ...

enquiry_dml.php

<?php

function insert()
{
      global $HTTP_SERVER_VARS, $HTTP_GET_VARS, $HTTP_POST_VARS, $HTTP_POST_FILES, $Translation;
      
      if(get_magic_quotes_gpc())
      {
            $enqDateStamp = $HTTP_POST_VARS["enqDateStamp"];
            $enqUsername = $HTTP_POST_VARS["enqUsername"];
            $city = $HTTP_POST_VARS["city"];
            $state = $HTTP_POST_VARS["state"];
            $postcode = $HTTP_POST_VARS["postcode"];
      }
      else
      {
            $enqDateStamp = addslashes($HTTP_POST_VARS["enqDateStamp"]);
            $enqUsername = addslashes($HTTP_POST_VARS["enqUsername"]);
            $city = addslashes($HTTP_POST_VARS["city"]);
            $state = addslashes($HTTP_POST_VARS["state"]);
            $postcode = addslashes($HTTP_POST_VARS["postcode"]);
      }
      
      sql("insert into tblEnquiries (city, state, postcode) values ("  . (($city != "") ? "'$city'" : "NULL") . ", " . (($state != "") ? "'$state'" : "NULL") . ", " . (($postcode != "") ? "'$postcode'" : "NULL") . ")");
      return mysql_insert_id();
}


function update($selected_id)
{
      global $HTTP_SERVER_VARS, $HTTP_GET_VARS, $HTTP_POST_VARS, $Translation;
      
      if(get_magic_quotes_gpc())
      {
            $enqDateStamp = $HTTP_POST_VARS["enqDateStamp"];
            $enqUsername = $HTTP_POST_VARS["enqUsername"];
            $city = $HTTP_POST_VARS["city"];
            $state = $HTTP_POST_VARS["state"];
            $postcode = $HTTP_POST_VARS["postcode"];
      }
      else
      {
            $enqDateStamp = addslashes($HTTP_POST_VARS["enqDateStamp"]);
            $enqUsername = addslashes($HTTP_POST_VARS["enqUsername"]);
            $city = addslashes($HTTP_POST_VARS["city"]);
            $state = addslashes($HTTP_POST_VARS["state"]);
            $postcode = addslashes($HTTP_POST_VARS["postcode"]);
      }

      sql("update tblEnquiries set " . "city=" . (($city != "") ? "'$city'" : "NULL") . ", " . "state=" . (($state != "") ? "'$state'" : "NULL") . ", " . "postcode=" . (($postcode != "") ? "'$postcode'" : "NULL") . " where enquiries_id='$selected_id'");
}

function form($selected_id = "", $AllowUpdate = 1, $AllowInsert = 1, $AllowDelete = 1)
{
      // function to return an editable form for a table records
      // and fill it with data of record whose ID is $selected_id. If $selected_id
      // is empty, an empty form is shown, with only an 'Add New'
      // button displayed.
      
      global $Translation;
      
      if(!$AllowInsert && $selected_id==""){  return ""; }
      
      
      // combobox: city
      $combo_city = new DataCombo;
      $combo_city->Query = "select postcodes_id, city, state, postcode from tblPostcodes order by city";
      $combo_city->SelectName = "city";

      if($selected_id)
      {
            $res = sql("select * from tblEnquiries where enquiries_id='$selected_id'");
            $row = mysql_fetch_array($res);
            $combo_state->SelectedData = $row["state"];
            $combo_postcode->SelectedData = $row["postcode"];
      }
      $combo_city->Render();
                $combo_state->Render();
                $combo_postcode->Render();

      
      // code for template based detail view forms
      
      // open the detail view template
      $templateCode=@implode('', @file('./tblEnquiries_templateDV.html'));
      
      // process form title
      $templateCode=str_replace('<%%DETAIL_VIEW_TITLE%%>', 'Enquiries detailed view', $templateCode);
      // process buttons
      if($AllowInsert){
            $templateCode=str_replace('<%%INSERT_BUTTON%%>', "<input type=image src=insert.gif name=insert alt='" . $Translation['add new record'] . "'>", $templateCode);
      }else{
            $templateCode=str_replace('<%%INSERT_BUTTON%%>', '', $templateCode);
      }
      if($selected_id){
            if($AllowUpdate){
                  $templateCode=str_replace('<%%UPDATE_BUTTON%%>', "<input type=image src=update.gif vspace=1 name=update alt='" . $Translation["update record"] . "'>", $templateCode);
            }else{
                  $templateCode=str_replace('<%%UPDATE_BUTTON%%>', '', $templateCode);
            }
            if($AllowDelete){
                  $templateCode=str_replace('<%%DELETE_BUTTON%%>', "<input type=image src=delete.gif vspace=1 name=delete alt='" . $Translation['delete record'] . "' onClick=\"return confirm('" . $Translation['are you sure?'] . "');\">", $templateCode);
            }else{
                  $templateCode=str_replace('<%%DELETE_BUTTON%%>', '', $templateCode);
            }
            $templateCode=str_replace('<%%DESELECT_BUTTON%%>', "<input type=image src=deselect.gif vspace=1 name=deselect alt='" . $Translation['deselect record'] . "'>", $templateCode);
      }else{
            $templateCode=str_replace('<%%UPDATE_BUTTON%%>', '', $templateCode);
            $templateCode=str_replace('<%%DELETE_BUTTON%%>', '', $templateCode);
            $templateCode=str_replace('<%%DESELECT_BUTTON%%>', '', $templateCode);
      }
      
      // process combos
      $templateCode=str_replace('<%%COMBO(city)%%>', $combo_city->HTML, $templateCode);
      $templateCode=str_replace('<%%COMBOTEXT(city)%%>', $combo_city->MatchText, $templateCode);
      $templateCode=str_replace('<%%COMBO(state)%%>', $combo_state->HTML, $templateCode);
      $templateCode=str_replace('<%%COMBOTEXT(state)%%>', $combo_state->MatchText, $templateCode);
      $templateCode=str_replace('<%%COMBO(postcode)%%>', $combo_postcode->HTML, $templateCode);
      $templateCode=str_replace('<%%COMBOTEXT(postcode)%%>', $combo_postcode->MatchText, $templateCode);
      
      // process images
      $templateCode=str_replace('<%%UPLOADFILE(enquiries_id)%%>', '', $templateCode);
      $templateCode=str_replace('<%%UPLOADFILE(enqDateStamp)%%>', '', $templateCode);
      $templateCode=str_replace('<%%UPLOADFILE(enqUsername)%%>', '', $templateCode);
      $templateCode=str_replace('<%%UPLOADFILE(city)%%>', '', $templateCode);
      $templateCode=str_replace('<%%UPLOADFILE(state)%%>', '', $templateCode);
      $templateCode=str_replace('<%%UPLOADFILE(postcode)%%>', '', $templateCode);
      
      // process values
      if($selected_id){
            $templateCode=str_replace('<%%VALUE(enquiries_id)%%>', htmlspecialchars($row['enquiries_id'], ENT_QUOTES), $templateCode);
            $templateCode=str_replace('<%%VALUE(enqDateStamp)%%>', htmlspecialchars($row['enqDateStamp'], ENT_QUOTES), $templateCode);
            $templateCode=str_replace('<%%VALUE(city)%%>', htmlspecialchars($row['city'], ENT_QUOTES), $templateCode);
            $templateCode=str_replace('<%%VALUE(state)%%>', htmlspecialchars($row['state'], ENT_QUOTES), $templateCode);
            $templateCode=str_replace('<%%VALUE(postcode)%%>', htmlspecialchars($row['postcode'], ENT_QUOTES), $templateCode);
      }else{
            $templateCode=str_replace('<%%VALUE(enquiries_id)%%>', '', $templateCode);
            $templateCode=str_replace('<%%VALUE(enqDateStamp)%%>', '', $templateCode);
            $templateCode=str_replace('<%%VALUE(city)%%>', '', $templateCode);
            $templateCode=str_replace('<%%VALUE(state)%%>', '', $templateCode);
            $templateCode=str_replace('<%%VALUE(postcode)%%>', '', $templateCode);
      }
      
      // process translations
      foreach($Translation as $symbol=>$trans){
            $templateCode=str_replace("<%%TRANSLATION($symbol)%%>", $trans, $templateCode);
      }
      
      // finally, clear scrap
      $templateCode=str_replace('<%%', '<!--', $templateCode);
      $templateCode=str_replace('%%>', '-->', $templateCode);

      return $templateCode;
}
?>

enquiry_form.html

<br>
<table border=1 bordercolor=navy cellpadding=0 cellspacing=0>
      <tr>
            <td>
                  <div class=TableTitle><%%DETAIL_VIEW_TITLE%%></div>
                  </td>
            </tr>
      <tr>
            <td>
                  <table>
                        <tr>
                              <td colspan=2></td>
                              <td rowspan=6 valign=top>
                                    <div><%%UPDATE_BUTTON%%></div>
                                    <div><%%DELETE_BUTTON%%></div>
                                    <div><%%DESELECT_BUTTON%%></div>
                                    <br>
                                    <div><%%INSERT_BUTTON%%></div>
                                    </td>
                              </tr>
                                                <tr>
                              <td class=TableHeader valign=top>
                                    <div class=TableHeader style="text-align:right;">City / suburb</div>
                                    </td>
                              <td class=TableBody width=300><%%COMBO(city)%%>&nbsp;&nbsp;</td>
                              </tr>
                        <tr>
                              <td class=TableHeader valign=top>
                                    <div class=TableHeader style="text-align:right;">State / territory</div>
                                    </td>
                              <td class=TableBody width=300><input size=50 type=text class=TextBox name=city value="<%%VALUE(state)%%>">&nbsp;&nbsp;</td>
                              </tr>
                        <tr>
                              <td class=TableHeader valign=top>
                                    <div class=TableHeader style="text-align:right;">Postcode</div>
                                    </td>
                              <td class=TableBody width=300><input size=50 type=text class=TextBox name=postcode value="<%%VALUE(postcode)%%>">&nbsp;&nbsp;</td>
                              </tr>
                                                </table>
                  </td>
            </tr>
      </table>