C#中DataTable中的Compute方法使用收集

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datataletable.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isnullcolumn.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 whencolumn.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