Display further details of retreived data in a text field

I have a drop down menu (list) and a textfield. The drop down menu displays all the schools in the database and the textfield will display the schoolcode. Currently, i am able to display all the schools, however, i need to know how to change the schoolcode (in a textfield) when i change the school (drop down menu). As in it changes automatically when i select the particular school.

eg: school abc with school code 123. when i select the school, it should as well change the school code in the textfield.. Pls help....

The codes i have now is:

<%
while(rs.next()){
site = rs.getString(1);
%>
<option value="School" selected> <%= site%> </option>
<%}
rs.close();
statement.close();
//connection.close();
%>


<%
while(rs2.next()){
String siteCode = rs2.getString(1);
%>
<td width="60%">School Code:
<input type="text" name="sn" value="<%= siteCode%>">
</td>
<%}
rs2.close();
statement2.close();
//connection.close();
%>


*Note: i am currently using 2 queries..

problem solved.
thanks....