DataTable相关操作，筛选，取前N条数据，获取指定列数据

#region DataTable筛选，排序返回符合条件行组成的新DataTable或直接用DefaultView按条件返回        /// <summary>        /// DataTable筛选，排序返回符合条件行组成的新DataTable或直接用DefaultView按条件返回        /// eg:SortExprDataTable(dt,"Sex='男'","Time Desc",1)        /// </summary>        /// <param name="dt">传入的DataTable</param>        /// <param name="strExpr">筛选条件</param>        /// <param name="strSort">排序条件</param>        /// <param name="mode">1,直接用DefaultView按条件返回,效率较高;2,DataTable筛选，排序返回符合条件行组成的新DataTable</param>        public static DataTable SortDataTable(DataTable dt, string strExpr, string strSort, int mode)        {            switch (mode)            {                case 1:                    //方法一　直接用DefaultView按条件返回                    dt.DefaultView.RowFilter = strExpr;                    dt.DefaultView.Sort = strSort;                    return dt;                case 2:                    //方法二　DataTable筛选，排序返回符合条件行组成的新DataTable                    DataTable dt1 = new DataTable();                    DataRow[] GetRows = dt.Select(strExpr, strSort);                    //复制DataTable dt结构不包含数据                    dt1 = dt.Clone();                    foreach (DataRow row in GetRows)                    {                        dt1.Rows.Add(row.ItemArray);                    }                    return dt1;                default:                    return dt;            }        }        #endregion        #region 获取DataTable前几条数据        /// <summary>        /// 获取DataTable前几条数据        /// </summary>        /// <param name="TopItem">前N条数据</param>        /// <param name="oDT">源DataTable</param>        /// <returns></returns>        public static DataTable DtSelectTop(int TopItem, DataTable oDT)        {            if (oDT.Rows.Count < TopItem) return oDT;            DataTable NewTable = oDT.Clone();            DataRow[] rows = oDT.Select("1=1");            for (int i = 0; i < TopItem; i++)            {                NewTable.ImportRow((DataRow)rows[i]);            }            return NewTable;        }        #endregion        #region 获取DataTable中指定列的数据        /// <summary>        /// 获取DataTable中指定列的数据        /// </summary>        /// <param name="dt">数据源</param>        /// <param name="tableName">新的DataTable的名词</param>        /// <param name="strColumns">指定的列名集合</param>        /// <returns>返回新的DataTable</returns>        public static DataTable GetTableColumn(DataTable dt, string tableName, params string[] strColumns)        {            DataTable dtn = new DataTable();            if (dt == null)            {                throw new ArgumentNullException("参数dt不能为null");            }            try            {                dtn = dt.DefaultView.ToTable(tableName, true, strColumns);            }            catch (Exception e)            {                throw new Exception(e.Message);            }            return dtn;        }        #endregion