System.Data.DataTable计算功能详解

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
             // 作者blog:      http://blog.csdn.net/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^&^
           
            
            
        }

        


    }
}