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。

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