使用Linq获取字段中具有重复值的最后N个行 [英] Using Linq to get the last N number of rows that have duplicated values in a field

问题描述

给定一个数据库表，一个列名C和一个大于1的数字N，我如何才能得到一组具有等于C列且至少具有N行的值的行?如果存在多个这样的组，则需要获取包含最新条目(具有最大ID的组)的组.

Given a database table, a column name C, and a number N larger than 1, how can I get a group of rows with equal values of column C which has at least N rows? If there exists more than one such group, I need to get the group which contains the newest entry (the one with the largest Id).

是否可以使用LINQ to Entities来做到这一点?

Is it possible to do this using LINQ to Entities?

Example:

> Id | Mycolumn
> - - - - - - -  
> 1 | name55555
> 2 | name22
> 3 | name22
> 4 | name22
> 5 | name55555
> 6 | name55555
> 7 | name1

Primary Key: ID
OrderBy: ID
Repeated column: Mycolumn

如果N = 3和C = Mycolumn，那么我们需要获取具有MyColumn列重复至少3次的行.

If N = 3 and C = Mycolumn, then we need to get rows which have the column MyColumn duplicated at least 3 times.

对于上面的示例，它应该返回第1、5和6行，因为name55555的最后一个索引是6，而name22的最后一个索引(也重复了3次)是4.

For the example above, it should return rows 1, 5 and 6, because last index of name55555 is 6, and last index of name22 (which is also repeated 3 times) is 4.

推荐答案

data.Mytable
    .OrderByDescending(m => m.Id)
    .GroupBy(m => m.Mycolumn)
    .FirstOrDefault(group => group.Count() >= N)
    .Take(N)
    .Select(m => m.Id)

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