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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
namespace Console11
{
??? class Program
??? {
??????? static void Main(string[] args)
??????? {
??????????? 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);
??????????? string a = "123";
??????????? System.Double b=123;
??????????? decimal c=123m;
??????????? Console.WriteLine((float)a);
??????????? //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报错，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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