Question

我想在我的DataTable中应用以下Sql查询

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

有关详细信息，请参阅此Question

Answer 1

类似的东西：

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);
}

请注意，在数据库服务器上进行聚合通常比通过网络填充DataTable然后聚合DataTable更有效。

Answer 2

您正在寻找DataTable.Compute。该方法可以为您计算聚合函数。所以你会得到类似的东西：

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

要按列进行分组，请参阅此问题：Efficient DataTable Group By。它提供了Linq实现以及“非Linq”实现。

Answer 3

使用 System.Data.DataSetExtensions 并尝试类似这样的内容

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

如何在C＃DataTable中使用sql Aggregate函数

3 个答案: