DataTable的計算功能)

C#--詳解DataTable的計算功能  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 table = new DataTable();

  //計算常量，可以沒有初始化列
  object test = table.Compute("1+1", "");
  Console.WriteLine(test);
  //test=2;

  test = table.Compute("1+1", "false");
  Console.WriteLine(test);
  //test=2;常數計算和filter無關

  test = table.Compute("abs(1)", "");
  Console.WriteLine(test);
  //test=null，不知道為這個什麼沒有抱錯，而且返回null,其他的數學函數都會抱錯

  test = table.Compute("2%2", "");
  Console.WriteLine(test);
  //test=0;
  //其他函數參考下面的計算資料行

  //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");
  ////拋出異常，這裡必須是彙總函式

  //*************************************支援的彙總函式**********************//
   
  //求數量
  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)","");
  ////拋出異常，這裡不能是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;

  //統計標準差
  test = table.Compute("StDev(value)", "");
  Console.WriteLine(test);
  //test=3.02765035409749

  //統計方差
  test = table.Compute("Var(value)", "");
  Console.WriteLine(test);
  //test=9.16666666666667

  //複雜計算
  test = table.Compute("max(value)/sum(value)", "");
  Console.WriteLine(test);
  //test=0.181818181818182
 
  /*******************************************計算資料行*************************/

  System.Data.DataColumn column = new DataColumn("exp1",typeof(float));
  table.Columns.Add(column);

  //簡單計算
  column.Expression = "value*2";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=2;

  //字串函數
  column.Expression = "len(id)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=3;

  //字串函數
  column.Expression = "len(' '+id+' ')";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=5;

  //字串函數
  column.Expression = "len(trim(' '+id+' '))";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=3;

  //字串函數
  column.Expression = "substring(id,3,len(id)-2)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=1; //substring的起始字元位置為1不是0

  //類型轉換
  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;

  //相當於sqlserver的isnull
  column.Expression = "isnull(value,10)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=1;

  //三元運算子,相當於sqlserver的case when
  column.Expression = "iif(value>5,1000,2000)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=2000;

  //like運算子
  column.Expression = "iif(id like '%1',1000,2000)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=1000;

  //in運算子
  column.Expression = "iif(id not in('id1'),1000,2000)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=2000;

  //嵌套的三元運算
  column.Expression = "iif(value>5,1000,iif(id like '%1',4000,2000))";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=4000;

  //用戶端計算所佔總數的百分比
  column.Expression = "value/sum(value)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=0.01818182 

  //用戶端計算差值,比如nba常規賽的勝場差
  column.Expression = "max(value)-value";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=9

   
  //***********************父子表計算*************************************/

  //初始化子表,父子表關係
  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);
  }

  //計運算元表記錄數
  column.Expression = "count(child(relation).value)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=10;
   

  //計算父子表的百分比
  column.Expression = "value/sum(child(relation).value)";
  test = table.Select("id='id1'")[0]["exp1"];
  Console.WriteLine(test);
  //test=0.01818182;

  //計算父子表的差值,比如父表為庫存數量，子表為訂購數量，計算得出需要補充的數量
  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;

  //比較遺憾的是沒有發現能夠計算同比和環比的方法，而且計算資料行無法作為約束
  //************結束，DataTable可以讓你盡量發揮聰明才智來減少繁雜的sql語句並且減輕伺服器計算符合^&^
   
   
   
  }

   

  }
}