转载 C#中DataTable中的Compute方法使用收集

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
巴特西

转载 C#中DataTable中的Compute方法使用收集

最新文章

热门文章
