C#中DataTable中的Compute方法使用收集

Compute函數的參數就兩個：Expression，和Filter。

Expresstion是計算運算式，關於Expression的詳細內容請看這裡“http://msdn2.microsoft.com/zh-cn/library/system.data.datacolumn.expression(VS.80).aspx”。而Filter則是條件過濾器，類似sql的Where條件。

        DataTable dt = new DataTable();        //嵌套的三元運算 牛叉到五體投地        object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);        Response.Write(obj);        System.Data.DataTable table = new DataTable();        //計算常量，可以沒有初始化列        object test = table.Compute("1+1", "");        Console.WriteLine(test);        string a = "123";        System.Double b = 123;        decimal c = 123m;        Console.WriteLine(Convert.ToDecimal(a));        //test=2;        test = table.Compute("1+1", "false");        Console.WriteLine(test);        //test=2;常數計算和filter無關        test = table.Compute("abs(1)", "");        Console.WriteLine(test);        //test=null，不知道為這個什麼沒有報錯，而且返回null,其他的數學函數都會抱錯        test = table.Compute("2%2", "");        Console.WriteLine(test);        //test=0;        //其他函數參考下面的計算資料行        //初始化datatale        table.Columns.Add("id", typeof(string));        table.Columns.Add("value", typeof(int));        for (int i = 1; i <= 10; i++)        {            System.Data.DataRow dRow = table.NewRow();            dRow["id"] = "id" + i.ToString();            dRow["value"] = i;            table.Rows.Add(dRow);        }        //test = table.Compute("value+1", "true");        /**/        ////拋出異常，這裡必須是彙總函式        //*************************************支援的彙總函式**********************//        //求數量        test = table.Compute("count(id)", "false");        Console.WriteLine(test);        //test=0;        test = table.Compute("count(id)", "true");        Console.WriteLine(test);        //test=10;        //求和        test = table.Compute("sum(value)", "");        Console.WriteLine(test);        //test=55;        //test = table.Compute("sum(id)","");        /**/        ////拋出異常，這裡不能是string        //平均        test = table.Compute("avg(value)", "");        Console.WriteLine(test);        //test=5;        //最小        test = table.Compute("min(value)", "");        Console.WriteLine(test);        //test=1;        //最大        test = table.Compute("max(value)", "");        Console.WriteLine(test);        //test=10;        //統計標準差        test = table.Compute("StDev(value)", "");        Console.WriteLine(test);        //test=3.02765035409749        //統計方差        test = table.Compute("Var(value)", "");        Console.WriteLine(test);        //test=9.16666666666667        //複雜計算        test = table.Compute("max(value)/sum(value)", "");        Console.WriteLine(test);        //test=0.181818181818182        /**/        /*******************************************計算資料行*************************/        System.Data.DataColumn column = new DataColumn("exp1", typeof(float));        table.Columns.Add(column);        //簡單計算        column.Expression = "value*2";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=2;        //字串函數        column.Expression = "len(id)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=3;        //字串函數        column.Expression = "len(' '+id+' ')";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=5;        //字串函數        column.Expression = "len(trim(' '+id+' '))";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=3;        //字串函數        column.Expression = "substring(id,3,len(id)-2)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=1; //substring的起始字元位置為1不是0        //類型轉換        column.Expression = "convert(substring(id,3,len(id)-2),'System.Int32')*1.6";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=1.6;        //相當於sqlserver的isnull        column.Expression = "isnull(value,10)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=1;        //三元運算子,相當於sqlserver的case when        column.Expression = "iif(value>5,1000,2000)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=2000;        //like運算子        column.Expression = "iif(id like '%1',1000,2000)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=1000;        //in運算子        column.Expression = "iif(id not in('id1'),1000,2000)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=2000;        //嵌套的三元運算        column.Expression = "iif(value>5,1000,iif(id like '%1',4000,2000))";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=4000;        //用戶端計算所佔總數的百分比        column.Expression = "value/sum(value)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=0.01818182        //用戶端計算差值,比如nba常規賽的勝場差        column.Expression = "max(value)-value";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=9        //***********************父子表計算*************************************/        //初始化子表,父子表關係        DataTable tableChild = new DataTable();        tableChild.Columns.Add("id", typeof(string));        tableChild.Columns.Add("value", typeof(int));        System.Data.DataSet ds = new DataSet();        ds.Tables.Add(tableChild);        ds.Tables.Add(table);        DataRelation relation = new DataRelation("relation", table.Columns["id"], tableChild.Columns["id"]);        ds.Relations.Add(relation);        for (int i = 1; i <= 10; i++)        {            System.Data.DataRow dRow = tableChild.NewRow();            dRow["id"] = "id1";            dRow["value"] = i;            tableChild.Rows.Add(dRow);        }        //計運算元表記錄數        column.Expression = "count(child(relation).value)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=10;        //計算父子表的百分比        column.Expression = "value/sum(child(relation).value)";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=0.01818182;        //計算父子表的差值,比如父表為庫存數量，子表為訂購數量，計算得出需要補充的數量        column.Expression = "iif(value-sum(child(relation).value)>0,0,value-sum(child(relation).value))";        test = table.Select("id='id1'")[0]["exp1"];        Console.WriteLine(test);        //test=-54;        //比較遺憾的是沒有發現能夠計算同比和環比的方法，而且計算資料行無法作為約束        //結束，DataTable可以讓你盡量發揮聰明才智來減少繁雜的sql語句並且減輕伺服器計算符合