字符串直接计算结果（datatable）

快来打我* 2023-05-31 06:46 72阅读 0赞

DataTable dt = new DataTable();
                        var Result= dt.Compute("1+2*3+2", "");//将运算字符串转换成表达式运算
                        NumberTxt.Text = Result.ToString()

如果用c\#编译器来实现的话会很慢一次编译大约需要0.4秒，用datatable来实现的话，就是瞬间的事情了

DataTable dt = new DataTable();
    
    
            //嵌套的三元运算（iif判断）
            object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);
            Response.Write(obj);//计算常量，可以没有初始化列
            object test = table.Compute("1+1", "");
            Console.WriteLine(test);
      
            //计算绝对值
            test = table.Compute("abs(1)", "");
            Console.WriteLine(test);
          
       
            //求余数
            test = table.Compute("2%2", "");
            Console.WriteLine(test);
    
    
            //*************************************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