C#--详解DataTable的计算功能

代码

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 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^&^ 
        
          
          
        } 

      


    } 
} 
http://www.cnblogs.com/greatverve/archive/2009/07/14/1523505.html