select option using onchange event in php

[KeyraRa]

hi! i have a problem with my php code..
my question is by using these code..
--> how to make a state select then the branch will appear together if related?
hope my english is okay..hehe..

*negeri = state
*cawangan = branch

# if i select State JOHOR..auto the Branch of Johor will appear together..not all branch in Malaysia will appear..help me!!:'(

here my code:

<select name="NEGERI" class="select" id="NEGERI"> <option value ="0">-- Sila Pilih --</option> <?php
                    //$sql = "SELECT * FROM negeri where FLAG=1 ORDER BY negeri ASC";
                    $sql = "SELECT * FROM negeri WHERE  negeri_id = '".$NEGERI."'  FLAG=1 ORDER BY negeri ASC";
                    $result_groups = mysql_query($sql);
                    $result_group_member = mysql_numrows ($result_groups);
                    if($result_group_number > 0)  {
                        while ($myrow = mysql_fetch_array($result_group))  {
                        if ($NEGERI == $myrow["negeri_id"])
                            echo "<option value = ".$myrow["negeri_id"]." selected > ".$myrow["negeri"]."</option>\n";
                        else "<option value =".$myrow["negeri_id"].">".$myrow["negeri"]."</option\n";
                        }
                        }
                        ?>  
     # cawangan = branch  #
     <?
                 $sql2 = "SELECT * FROM negeri_cawangan WHERE  cawangan_id = '".$CAWANGAN."'  FLAG=1 ORDER BY cawangan ASC";
                 $result_groups2 = mysql_query($sql);
                 $result_group_number2 = mysql_numrows2($result_groups2);
                 if($result_group_number2 > 1) {
                 while ($myrow2 = mysql_fetch_array($result_groups2)) {
                    if ($CAWANGAN == $myrow2["cawangan_id"])
                    echo "<option value=".$myrow2["cawangan_id"]." selected > ".$myrow["cawangan"]."</option>\n";
                    else
                    echo "<option value = ".$myrow2["cawangan_id"]." > ".$myrow2["cawangan"]."</option>\n";
                    }
                    }
                    ?>

another question:
- where should i put the onchange event in this code?

[Dormilich]

where should i put the onchange event in this code?

in the JavaScript file.

how to make a state select then the branch will appear together if related?

you have to either fetch the according branch once the user selects the state or remove all unrelated branches from the list.

[KeyraRa]

the branch and state have a own code.

*for state:
eg: JOHOR(01)
KEDAH (02)

*for branch:
eg: 01021011 JOHOR BAHRU
07041011 GEORGETOWN

1) so now in my code..where should i call the function?
2)how to write a onchange event and function call?
3)in Malaysia have many branch of each state..so should I write all the name of state and branch each? do you have a simple way?