DataTable dtGroup = dv.ToTable(true, new string[] {"a1", "ID", "EN", "UA", "HU", "RU", "Docs_Doc_Number", "Revision", "Revision_Date", "Author_Name", "Owner_Position", "Doc_Description", "Work_Place", "ForButtons" });

commandText = @"SELECT *, 'a' as a1 "
                   + @"FROM xxx ";

dtGroup.Columns.Add("a1");

if (!dtGroup.Columns.Contains("a1"))
{
     dtGroup.Columns.Add(new DataColumn("a1"));
     dtGroup.Columns["a1"].SetOrdinal(0); 
}