Display in Textbox from database using Drop Down list...

Hello friends,
I am a beginner.Please help for the following content
I created a table (Workers) with two columns(username,userid)...


Now i have Dropdownlist and textbox.


Dropdownlist for Userid,
Textbox for Username.


If i click on the userid in dropdownlist, then the particular username should get displayed on the textbox....
For this i have tried codings...please help me to finish it...






private void DropDownList()
    {
        OleDbConnection databaseConnection = new OleDbConnection(ConfigurationManager.ConnectionStrings[1].ConnectionString);
        databaseConnection.Open();
        OleDbDataAdapter dataAdapter = new OleDbDataAdapter("Select userid from workers", database ...