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^&^











}











}


}