过滤DataTable中的指定字段重复的行

  #region   过滤DataTable中的指定字段重复的行

        ///   <summary> 
        ///   过滤DataTable中的指定字段重复的行 
        ///   </summary> 
        ///   <param   name= "dt "> </param> 
        ///   <param   name= "FieldName "> </param> 
        ///   <returns> </returns> 
        public DataTable SelectDistinctByField(DataTable dt, string FieldName)
        {
            DataTable returnDt = new DataTable();
            returnDt = dt.Copy();//将原DataTable复制一个新的 
            DataRow[] drs = returnDt.Select(" ", FieldName);//将DataTable按指定的字段排序 
            object LastValue = null;
            for (int i = 0; i < drs.Length; i++)
            {
                if ((LastValue == null) || (!(ColumnEqual(LastValue, drs[i][FieldName]))))
                {
                    LastValue = drs[i][FieldName];
                    continue;
                }

                drs[i].Delete();
            }

            return returnDt;
        }

        private bool ColumnEqual(object A, object B)
        {
            //   Compares   two   values   to   see   if   they   are   equal.   Also   compares   DBNULL.Value. 
            //   Note:   If   your   DataTable   contains   object   fields,   then   you   must   extend   this 
            //   function   to   handle   them   in   a   meaningful   way   if   you   intend   to   group   on   them. 

            if (A == DBNull.Value && B == DBNull.Value)   //     both   are   DBNull.Value 
                return true;
            if (A == DBNull.Value || B == DBNull.Value)   //     only   one   is   DBNull.Value 
                return false;
            return (A.Equals(B));     //   value   type   standard   comparison 
        }

        #endregion