DataTable直接进行计算

经常需要从数据库取得查询结果，然后进行逻辑处理后再在页面展示，所以直接使用datatable的计算功能，无疑会方便很多，并且有时效率也很高。

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using

 System;

using  System.ComponentModel;

using  System.Data;

using  System.Windows.Forms;

namespace  WindowsApplication1

... {

    public partial class Form1 : Form

    ...{

        

        public Form1()

        ...{

            InitializeComponent();

        }

       

        private void button1_Click(object sender, EventArgs e)

        ...{

            //System.Data.DataTable计算功能详解，转载请保留以下信息

            //测试环境      vs2005,c#

            //作者:         jinjazz

       

           

            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);

            //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抱错，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^&^

           

            

            

        }

        

    }

}