DataTable.Compute方法使用实例

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();

//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((float)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^&^

}
    }
}

DataTable求平均值，最大值，最小值

DataTable dsValue;

if (dsValue.Rows.Count > 0)

            {

                maxValue = float.Parse(dsValue.Compute("max([" + ParaName + "])", "" ).ToString());

                minValue = float.Parse(dsValue.Compute("min([" + ParaName + "])", "" ).ToString());

                avgValue = float.Parse(dsValue.Compute("avg([" + ParaName + "])", "" ).ToString());

                SDAVG = float.Parse(dsValue.Compute("avg([" + SDVALUE + "])", "" ).ToString());//设定平均

               

                if (avgValue.ToString() != string.Empty && SDAVG.ToString() != string.Empty)

                {

                    sszavg_sdzavg_subValue = Math.Abs(SDAVG - avgValue);

                }

                try

                {

                    sdValue = float.Parse(dsValue.Compute("StDev([" + ParaName + "])", "" ).ToString());

                }

                catch (Exception ex)

                {

                    sdValue = 0;

                }

            }