DataTable.Compute方法使用实例

最新推荐文章于 2024-10-11 19:00:45 发布

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最新推荐文章于 2024-10-11 19:00:45 发布

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文章标签：数据库

本文介绍如何利用DataTable实现复杂的数据计算和管理任务，包括常量计算、数学函数应用、聚合函数使用、计算列操作及父子表计算等，展示其在减少SQL语句、减轻服务器计算负荷方面的优势。

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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();

//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^&^

}