C#中DataTable中的Compute方法使用收集

原文：https://blog.csdn.net/smartsmile2012/article/details/8309664

Compute函数的参数就两个：Expression，和Filter。

Expresstion是计算表达式，关于Expression的详细内容请看这里“http://msdn2.microsoft.com/zh-cn/library/system.data.datacolumn.expression(VS.80).aspx”。而Filter则是条件过滤器，类似sql的Where条件。

        DataTable dt = new DataTable();




        //嵌套的三元运算 牛叉到五体投地




        object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);




        Response.Write(obj);




 




 




        System.Data.DataTable table = new DataTable();




        //计算常量，可以没有初始化列




        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;常数计算和filter无关




 




        test = table.Compute("abs(1)", "");




        Console.WriteLine(test);




        //test=null，不知道为这个什么没有报错，而且返回null,其他的数学函数都会抱错




 




        test = table.Compute("2%2", "");




        Console.WriteLine(test);




        //test=0;




        //其他函数参考下面的计算列




 




 




 




        //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");




        /**/




        ////抛出异常，这里必须是聚合函数




 




 




 




        //*************************************支持的聚合函数**********************//




 




        //求数量




        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)","");




        /**/




        ////抛出异常，这里不能是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;




 




        //统计标准偏差




        test = table.Compute("StDev(value)", "");




        Console.WriteLine(test);




        //test=3.02765035409749




 




        //统计方差




        test = table.Compute("Var(value)", "");




        Console.WriteLine(test);




        //test=9.16666666666667




 




 




        //复杂计算




        test = table.Compute("max(value)/sum(value)", "");




        Console.WriteLine(test);




        //test=0.181818181818182




 




        /**/




        /*******************************************计算列*************************/




 




        System.Data.DataColumn column = new DataColumn("exp1", typeof(float));




        table.Columns.Add(column);




 




 




        //简单计算




        column.Expression = "value*2";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=2;




 




        //字符串函数




        column.Expression = "len(id)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=3;




 




        //字符串函数




        column.Expression = "len(' '+id+' ')";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=5;




 




        //字符串函数




        column.Expression = "len(trim(' '+id+' '))";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=3;




 




        //字符串函数




        column.Expression = "substring(id,3,len(id)-2)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=1; //substring的起始字符位置为1不是0




 




        //类型转换




        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;




 




        //相当于sqlserver的isnull




        column.Expression = "isnull(value,10)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=1;




 




        //三元运算符,相当于sqlserver的case when




        column.Expression = "iif(value>5,1000,2000)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=2000;




 




        //like运算符




        column.Expression = "iif(id like '%1',1000,2000)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=1000;




 




        //in运算符




        column.Expression = "iif(id not in('id1'),1000,2000)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=2000;




 




        //嵌套的三元运算




        column.Expression = "iif(value>5,1000,iif(id like '%1',4000,2000))";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=4000;




 




 




        //客户端计算所占总数的百分比




        column.Expression = "value/sum(value)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=0.01818182




 




 




        //客户端计算差值,比如nba常规赛的胜场差




        column.Expression = "max(value)-value";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=9




 




 




        //***********************父子表计算*************************************/




 




 




        //初始化子表,父子表关系




        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);




        }




 




 




        //计算子表记录数




        column.Expression = "count(child(relation).value)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=10;




 




 




 




        //计算父子表的百分比




        column.Expression = "value/sum(child(relation).value)";




        test = table.Select("id='id1'")[0]["exp1"];




        Console.WriteLine(test);




        //test=0.01818182;




 




 




        //计算父子表的差值,比如父表为库存数量，子表为订购数量，计算得出需要补充的数量




        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;




 




        //比较遗憾的是没有发现能够计算同比和环比的方法，而且计算列无法作为约束




        //结束，DataTable可以让你尽量发挥聪明才智来减少繁杂的sql语句并且减轻服务器计算符合