Problems when user enter the field

Question

I have problem when user enter the field, but it cannot retrieve from the table. Below is my program, help me to check is it correct or not, THANKS
<input type="text" name="po_num<%=i%>" style="width:100%;text-align:left;" onChnage="chkPOexist(<%=i%>)">
Function chkPOexist(i){
if documen.all.po_num.value == null {
alert ("PO cannot be null");
else {
po_num = new String;
po_num = eval(document.po_num[i].value)
alert(po_num);
<% System.out.println("PP " +po_num);
sql_query = "SELECT po_num"+
" FROM pomast"+
" WHERE po_num '"+po_num+"' ";
                    try{
                    rset = db.execSQL(sql_query);
                    catch(SQLException e) {
                    System.err.println("Error in query");
                    while(rset.next()== true){
po_num = rset.getString("po_num");
%>
</select value="<%=po_num%>"><%=po_num%></select>
                    <%}%>

Answer 1

You seem to have some confusion between java and javascript, and when they run.
Java code runs only on the server, and produces an HTML page.
Javascript code runs on the client.
The two can not communicate. Specific to your example you seem to think that the java code will be executed by your onChange event.
This is not the case.
In order to run java code again you have make a request by submitting the form, or clicking on a link.
Cheers,
evnafets