csharp: DataTable結構相同的比較

       /// <summary>
        /// DataTable分頁
        /// </summary>
        /// <param name="dt">DataTable</param>
        /// <param name="PageIndex">頁索引,注意：從1開始</param>
        /// <param name="PageSize">每頁大小</param>
        /// <returns></returns>
        public static DataTable GetPagedTable(DataTable dt, int currentPageIndex, int pageSize)
        {

            //1
            //判斷當前索引
            if (currentPageIndex == 0)
                return dt;
            //從數據集合拷貝數據
            DataTable newdt = dt.Copy();
            //數據清空
            newdt.Clear();
            //開始數據索引 = 當前頁-1 x 每頁大小
            int rowbegin = (currentPageIndex - 1) * pageSize;
            //結束數據索引 = 當前頁 x 每頁大小
            int rowend = currentPageIndex * pageSize;
            //開始數據索引 大於等於 當前數據集合大小
            if (rowbegin >= dt.Rows.Count)
                return newdt;
            //結束數據索引 大於 當前數據集合大小
            if (rowend > dt.Rows.Count)
                rowend = dt.Rows.Count;
            //遍歷數據
            for (int i = rowbegin; i <= rowend - 1; i++)
            {
                DataRow newdr = newdt.NewRow();
                DataRow dr = dt.Rows[i];
                foreach (DataColumn column in dt.Columns)
                {
                    newdr[column.ColumnName] = dr[column.ColumnName];
                }
                newdt.Rows.Add(newdr);
            }

            return newdt;


            //2
            //if (currentPageIndex == 0)
            //{
            //return dt;
            //}

            //DataTable newdt = dt.Clone();// dt.Copy();

            //int rowbegin = (currentPageIndex - 1) * pageSize;//當前頁的第一條數據在dt中的位置
            //int rowend = currentPageIndex * pageSize;//當前頁的最后一條數據在dt中的位置

            //if (rowbegin >= dt.Rows.Count)
            //{
            //    return newdt;
            //}

            //if (rowend > dt.Rows.Count)
            //{
            //    rowend = dt.Rows.Count;
            //}

            //DataView dv = dt.DefaultView;
            //for (int i = rowbegin; i <= rowend - 1; i++)
            //{
            //    newdt.ImportRow(dv[i].Row);
            //}

            //return newdt;

        }

        /// <summary>
        /// DataTable 結構相同的比較
        /// 
        /// C# datatable comparison  Same  Different
        /// 塗聚文
        /// </summary>
        /// <param name="first"></param>
        /// <param name="second"></param>
        /// <returns></returns>
        public DataTable CompareTables(DataTable first, DataTable second)
        {
            first.TableName = "FirstTable";

            second.TableName = "SecondTable";

            //Create Empty Table

            DataTable table = new DataTable("Difference");

            try
            {
                //Must use a Dataset to make use of a DataRelation object
                using (DataSet ds = new DataSet())
                {
                    ds.Tables.AddRange(new DataTable[] { first.Copy(), second.Copy() });

                    //Get Columns for DataRelation

                    DataColumn[] firstcolumns = new DataColumn[ds.Tables[0].Columns.Count];


                    for (int i = 0; i < firstcolumns.Length; i++)
                    {

                        firstcolumns[i] = ds.Tables[0].Columns[i];

                    }


                    DataColumn[] secondcolumns = new DataColumn[ds.Tables[1].Columns.Count];

                    for (int i = 0; i < secondcolumns.Length; i++)
                    {

                        secondcolumns[i] = ds.Tables[1].Columns[i];

                    }


                    //Create DataRelation

                    DataRelation r = new DataRelation(string.Empty, firstcolumns, secondcolumns, false);

                    ds.Relations.Add(r);

                    //Create columns for return table

                    for (int i = 0; i < first.Columns.Count; i++)
                    {

                        table.Columns.Add(first.Columns[i].ColumnName, first.Columns[i].DataType);

                    }


                    //If First Row not in Second, Add to return table.

                    table.BeginLoadData();



                    foreach (DataRow parentrow in ds.Tables[0].Rows)
                    {

                        DataRow[] childrows = parentrow.GetChildRows(r);

                        if (childrows == null || childrows.Length == 0)

                            table.LoadDataRow(parentrow.ItemArray, true);

                    }

                    table.EndLoadData();

                }
            }
            catch (Exception ex)
            {

                throw ex;

            }

            return table;
        }

 

USE pubs
GO

--使用帶有簡單 CASE 函數的 SELECT 語句
SELECT   Category = 
      CASE type
         WHEN 'popular_comp' THEN 'Popular Computing'
         WHEN 'mod_cook' THEN 'Modern Cooking'
         WHEN 'business' THEN 'Business'
         WHEN 'psychology' THEN 'Psychology'
         WHEN 'trad_cook' THEN 'Traditional Cooking'
         ELSE 'Not yet categorized'
      END,
   CAST(title AS varchar(25)) AS 'Shortened Title',
   price AS Price
FROM titles
WHERE price IS NOT NULL
ORDER BY type, price
COMPUTE AVG(price) BY type
GO

--使用帶有簡單 CASE 函數和 CASE 搜索函數的 SELECT 語句
 SELECT    'Price Category' = 
      CASE 
         WHEN price IS NULL THEN 'Not yet priced'
         WHEN price < 10 THEN 'Very Reasonable Title'
         WHEN price >= 10 and price < 20 THEN 'Coffee Table Title'
         ELSE 'Expensive book!'
      END,
   CAST(title AS varchar(20)) AS 'Shortened Title'
FROM titles
ORDER BY price
GO

--使用帶有 SUBSTRING 和 SELECT 的 CASE 函數
SELECT SUBSTRING((RTRIM(a.au_fname) + ' '+ 
   RTRIM(a.au_lname) + ' '), 1, 25) AS Name, a.au_id, ta.title_id,
   Type = 
  CASE 
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'BU' THEN 'Business'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'MC' THEN 'Modern Cooking'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'PC' THEN 'Popular Computing'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'PS' THEN 'Psychology'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'TC' THEN 'Traditional Cooking'
  END
FROM titleauthor ta JOIN authors a ON ta.au_id = a.au_id

--