Question

我有一个表tbLocations，其中包含以下列：

int           id      {PRIMARY_KEY, AUTO_INCREMENT}
int           userid  {Foreign key with table_users}
varchar(200)  location

在此表中，我有以下几行：

1, 1, New York
2, 1, California
3, 1, Seattle
4, 1, New York
5, 2, Seattle
6, 2, Ontario
7, 3, Chicago
8, 4, Las Vegas
9, 5, New York

我想创建一个C＃linq查询，该查询可以让我获得前10个位置，对于我而言，我应该得到

New York  2
Seattle   2

这里的问题是用户i.e. New York is duplicate for userid 1的位置可以重复，所以我不希望这样的重复影响最终报告。

就像在最终报告中一样，我的纽约= 2，而不是= 3

如何在LINQ中做到这一点？

我真的不知道从哪里开始，我通过分组进行了尝试，但是没有用

Answer 1

从此查询开始：

select top 10 count(*) cnt, [location] from 
     (
     select count(*) as dupl, userid, [location]
     from tbLocations
     group by userid,  [location]
     ) as test
 group by [location]
 order by cnt desc

这给出了以下结果：

cnt location
2   New York
2   Seattle
1   Ontario
1   California
1   Chicago
1   Las Vegas

Answer 2

这里是my solution：

var locations = new List<Location>
{
    new Location{ Id = 1, UserId = 1, Name = "New York" },
    new Location{ Id = 2, UserId = 1, Name = "California" },
    new Location{ Id = 3, UserId = 1, Name = "Seattle" },
    new Location{ Id = 4, UserId = 1, Name = "New York" },
    new Location{ Id = 5, UserId = 2, Name = "Seattle" },
    new Location{ Id = 6, UserId = 2, Name = "Ontario" },
    new Location{ Id = 7, UserId = 3, Name = "Chicago" },
    new Location{ Id = 8, UserId = 4, Name = "Las Vegas" },
    new Location{ Id = 9, UserId = 5, Name = "New York" },
};

var topLocations = locations
    .GroupBy(location => new { location.UserId, location.Name })
    .Select(group => group.First())
    .GroupBy(location => location.Name)
    .Select(group => new { group.Key, Count = group.Count() })
    .OrderByDescending(location => location.Count)
    .Take(2);

foreach (var item in topLocations)
{
    Console.WriteLine($"{item.Key} {item.Count}");
}

EF十大最受欢迎地点c＃

2 个答案: