ComboBoxes loaded by multiple SQL query?

In an attempt to eliminate much C# code, I would like to make the following code work.

It compiles fine but errors upon inital loading to run. It errors by reading the second ComboBox in the While statement.

I've combined SQL statements in C# elsewhere if I place a ; between the SQL syntax.....


private void LoadComboBoxes()
{
string SQL = " SELECT DISTINCT datetime FROM TimeClock ORDER BY datetime ASC ; " +
                   " SELECT DISTINCT  namefirst FROM TimeClock ORDER BY namefirst ASC ; " +
                   " SELECT DISTINCT  namelast FROM TimeClock ORDER BY namelast ASC " ;

cn = new SqlConnection((ConfigurationSettings.AppSettings["cn"]);
SqlDataAdapter da = new SqlDataAdapter(SQL,cn);
cn.Open();
SqlDataReader rdr = da.SelectCommand.ExecuteReader();

While(rdr.Read())
{
       cbxDateTime.Items.Add(rdr["datetime"].ToString());
       cbxNameFirst.Items.Add(rdr["namefirst"].ToString());  // ERROR
       cbxNameLast.Items.Add(rdr["namelast"].ToString());
}
rdr.Close();
cn.Close();