本文实例讲述了C# DataTable中Compute方法用法。分享给大家供大家参考，具体如下：
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测试数据/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。
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，不知道为什么这个没有报错，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
希望本文所述对大家C#程序设计有所帮助。
dy("nrwz");
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