System.Data.DataTable计算功能详解 收藏
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^&^ } } }
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