Domino / Db2: how to populate 2nd field based on previous field?

Hi all, I need a simple solution to my issue. I have a domino form called keyword. I have 2 fields in the form: Select Region: Region

Select Country: Country

In the WebQueryOpen event I am calling an agent to populate the ‘Region’ field from DB2 via LCConnection (“DB2”).

sqlst1 = {Select DISTINCT Region from DB2.REGIONTABLE order by Region}

For the country field:

sqlst2 = {Select CTRY_NAME from  DB2.REGIONTABLE Reg, DB2.Country Ctry WHERE Reg.Region ='} + doc.Region(0) + {' order by Ctry.CTRY_NAME}

My issue is: When you select the Region, how to filter and get show only country belongs to that region selected.

how do i acheive this result? Any help with sample would be appreciated. Have a nice day.