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<转> 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。
[csharp] view plaincopyprint?
- 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
<转> C#中DataTable中的Compute方法使用收集
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