我如何可以使用C＃的DataTable

Question

SQL聚合函數我想在應用follwing SQL查詢我的DataTable

SELECT MakeDistinct AS AfterDistinct 
     , COUNT(MakeDistinct) AS Count 
    FROM MyTable 
GROUP BY MakeDistinct 

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Answer 1

類似：

var query = from row in table.AsEnumerable() 
      group row by row.Field<int>("MakeDistinct") into grp 
      select new {AfterDistinct = grp.Key, Count = grp.Count()}; 

foreach(var row in query) { 
    Console.WriteLine("{0}: {1}", row.AfterDistinct, row.Count); 
} 

注意，在數據庫服務器聚合通常比在網絡上填充一個DataTable，然後聚集DataTable更加高效。

Answer 2

您是部分尋找DataTable.Compute。該方法可以爲您計算聚合函數。所以，你喜歡的東西：按列

object sumObject; 
sumObject = myDataTable.Compute("Sum(Count)", ""); // second parameter is the where clause 

對於分組，看到了這個問題：Efficient DataTable Group By。它提供了一個Linq實現以及一個「非Linq」實現。

Answer 3

使用System.Data.DataSetExtensions和嘗試這樣的事情

var result = from row in dt.AsEnumerable() 
       group row by row.Field<int>("MakeDistinct") into grp 
       select new 
       { 
        MakeDistinct = grp.Key, 
        Count = grp.Count() 
       };