DataTable.Compute方法使用執行個體
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using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data;namespace Console11{ class Program { static void Main(string[] args) { 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((float)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^&^ } }}
