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,EventArgse)
... {

// 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.youkuaiyun.com/jinjazz/


System.Data.DataTabletable = 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.DataRowdRow = 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.DataColumncolumn = 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casewhen
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(idlike'%1',1000,2000) " ;
test = table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
Console.WriteLine(test);
// test=1000;

// in运算符
column.Expression = " iif(idnotin('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(idlike'%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
DataTabletableChild = new DataTable();

tableChild.Columns.Add( " id " , typeof ( string ));
tableChild.Columns.Add( " value " , typeof ( int ));

System.Data.DataSetds = new DataSet();
ds.Tables.Add(tableChild);
ds.Tables.Add(table);
DataRelationrelation = new DataRelation( " relation " ,table.Columns[ " id " ],tableChild.Columns[ " id " ]);
ds.Relations.Add(relation);

for ( int i = 1 ;i <= 10 ;i ++ )
... {
System.Data.DataRowdRow = 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);
//