Here is the code..Hope it will help you..
string sqlQuery = "Select " + colName + ",0 as " + colValue + " Union Select " + colName + "," + colValue + " from " + tblName;
if (srchCodn != "")
{
sqlQuery += " " + srchCodn;
}
adp = new SqlDataAdapter(sqlQuery, conn);
tbl = new DataTable();
adp.Fill(tbl);
ddlList.DataSource = tbl;
ddlList.DataTextField = colName;
ddlList.DataValueField = colValue;
ddlList.DataBind();
After Binding ddlList you can get the value using ddlList.DataValueField.