合并datatable中指定字段重复的值

       数据库表中某一字段的值有重复，如果想让值不重复的显示出来，

        一、 最一般，最简单的办法就是在sql语句中筛选：select   distinct    字段名   from    表名

        二、 但是，如果只能从返回的datatable中筛选的话，也是可以实现的。

  /// <summary>        /// 合并datatable中指定的某重复的字段        /// </summary>        /// <param name="dt">要操作的datatable</param>        /// <param name="FieldName">字段名</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         }