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Compute函數的參數就兩個:Expression,和Filter。
Expresstion是計算運算式,關於Expression的詳細內容請看這裡“http://msdn2.microsoft.com/zh-cn/library/system.data.datacolumn.expression(VS.80).aspx”。而Filter則是條件過濾器,類似sql的Where條件。
[csharp] view plaincopyprint?
- DataTable dt = new DataTable();
- //嵌套的三元運算 牛叉到五體投地
- object obj = dt.Compute("iif(1000=5,1000,iif(100>100,4001,2000))", null);
- Response.Write(obj);
-
-
- System.Data.DataTable table = new DataTable();
- //計算常量,可以沒有初始化列
- 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報錯,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
<轉> C#中DataTable中的Compute方法使用收集