您的位置:首页 > c#开发技巧 >

System.Data.DataTable计算功能

2013-10-17 11:56 来源:未知编辑:admin点击:

本文根据一个实例着重介绍了System.Data.DataTable的计算功能,相信这篇文章定能为大家的工作和学习有所帮助。
  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#
  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;
  //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。
  }
  }
  }