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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
???????????? // 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,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',2000) " ;
????????????test? = ?table.Select( " id='id1' " )[ 0 ][ " exp1 " ];
????????????Console.WriteLine(test);
???????????? // test=1000;
???????????? // in运算符
????????????column.Expression? = ? " iif(id?not?in('id1'),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,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,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^&^
???????????
????????????
????????????
????????}
????????
????}
}
?
（编辑：李大同）
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