OnChange() event how does it work and what is the syntax

Question

hi,
i have a field (County) on a form in a jsp page that needs to get all its values from the database and present it to the user also i have another field (year) this also needs to get all its values as a drop down from the database.
i dont have any lib tag available to use and can't afford the time to set this up. so just have to script in jsp or use beans in jsp.
my question is 2fold
Q1. - i was thinking of having a DataAccess (dA) object to run a sql to select * distict couties ...
also have another query in DataAccess select * Distinct year....
and in the jsp instantiate the (dA) and iterate through and fill the select drop down box - how to code this syntax i'm not sure and if this is the correct approach or the only approach would appreciate some sample code that i can mess around with thanks.
- is above approach best way of doing this. - also taking into account Q2.
Q2 - when the user selects county then i need to fire a onChange event - probably using javascript but not sure how this works - bascially i need to then update the year drop down according to the below sql-
again how is this possible - and is this the best approach or will it be too many calls to the database - especially consdering that the forms are all part of a search tool.
SELECT     DISTINCT     v.year
FROM          v_volumes     v
WHERE          v.county     = <the selected county>
OR          (v.county_reference     =
               (SELECT     ca.county_reference
                FROM          county_aliases     ca
                ,          counties     c
                WHERE     ca.county_reference_also_called     = c.county_reference
                AND          c.county     = <the selected county>)
ORDER BY v.year

Answer 1

Sorry to rain on your parade, but its not going to be quite that simple.
Populating a second dropdown depending on the first one, has been discussed quite in depth on this forum, I suggest you do a search to look at older posts.
Javascript code cannot call java/database code from an onclick event.
The best it can do is trigger a form submission, which reloads the page
running any java/sql code that displaying the page entails.
So onlick event on the first dropdown triggers a form submit, which loads the page with the correct values in the second dropdown.
con: requires a page request
The other approach is to download ALL possible values to the jsp page, and have javascript handle the swapping of values.
pro: no page refresh needed
con: must have all data available on the page. javascript is a bit more complicated.
Hope this helps,
evnafets