DataTable中使用计算的方法

System.Data.DataTable table = new DataTable(); //计算常量，可以没有初始化列 object objStr = table.Compute("1+1",""); Console.WriteLine(objStr); //objStr=2; objStr = table.Compute("1+1","false"); Console.WriteLine(objStr); //objStr=2;常数计算和filter无关 objStr = table.Compute("abs(1)",""); Console.WriteLine(objStr); //objStr=null，不知道为这个什么没有抱错，而且返回null,其他的数学函数都会抱错 objStr = table.Compute("2%2",""); Console.WriteLine(objStr); //objStr=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); } //objStr = 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 objStr = table.Compute("count(id)","false"); Console.WriteLine(objStr); //objStr=0; objStr = table.Compute("count(id)","true"); Console.WriteLine(objStr); //objStr=10; //求和 objStr = table.Compute("sum(value)",""); Console.WriteLine(objStr); //objStr=55; //objStr = table.Compute("sum(id)",""); /**/ ////抛出异常，这里不能是string //平均 objStr = table.Compute("avg(value)",""); Console.WriteLine(objStr); //objStr=5; //最小 objStr = table.Compute("min(value)",""); Console.WriteLine(objStr); //objStr=1; //最大 objStr = table.Compute("max(value)",""); Console.WriteLine(objStr); //objStr=10; //统计标准偏差 objStr = table.Compute("StDev(value)",""); Console.WriteLine(objStr); //objStr=3.02765035409749 //统计方差 objStr = table.Compute("Var(value)",""); Console.WriteLine(objStr); //objStr=9.16666666666667 //复杂计算 objStr = table.Compute("max(value)/sum(value)",""); Console.WriteLine(objStr); //objStr=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"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=2; //字符串函数 column.Expression = "len(id)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=3; //字符串函数 column.Expression = "len(' '+id+' ')"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=5; //字符串函数 column.Expression = "len(trim(' '+id+' '))"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=3; //字符串函数 column.Expression = "substring(id,3,len(id)-2)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=1; //substring的起始字符位置为1不是0 //类型转换 column.Expression = "convert(substring(id,len(id)-2),'System.Int32')*1.6"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=1.6; //相当于sqlserver的isnull column.Expression = "isnull(value,10)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=1; //三元运算符,相当于sqlserver的case when column.Expression = "iif(value>5,1000,2000)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=2000; //like运算符 column.Expression = "iif(id like '%1',2000)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=1000; //in运算符 column.Expression = "iif(id not in('id1'),2000)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=2000; //嵌套的三元运算 column.Expression = "iif(value>5,iif(id like '%1',4000,2000))"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=4000; //客户端计算所占总数的百分比 column.Expression = "value/sum(value)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=0.01818182 //客户端计算差值,比如nba常规赛的胜场差 column.Expression = "max(value)-value"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=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)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=10; //计算父子表的百分比 column.Expression = "value/sum(child(relation).value)"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=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,value-sum(child(relation).value))"; objStr = table.Select("id='id1'")[0]["exp1"]; Console.WriteLine(objStr); //objStr=-54;

（编辑：李大同）

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