Compute函数的参数就两个：Expression，和Filter。

Expresstion是计算表达式，关于Expression的详细内容请看这里“http://msdn2.microsoft.com/zh-cn/library/system.data.datacolumn.expression(VS.80).aspx”。而Filter则是条件过滤器，类似sql的Where条件。

DataTable dt = new DataTable();  //嵌套的三元运算 牛叉到五体投地  object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);  Response.Write(obj);      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(Convert.ToDecimal(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,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;    //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