我的用戶活動日誌看起來是這樣的：與LINQ
標識，用戶名，日期
我需要計算每日總條目數，當日最活躍的用戶爲最近10天。
//pseudo code
from entry in data.UserLogs
group by entry.Date == each day
select username of most active user, count(Id)
林LINQ和SQL的新來臨可以有人幫我完成這個查詢嗎？
我想這是你以後的樣子。只需拖放到LINQPad看到它在行動
void Main()
{
var logs = new List<UserLog>
{
new UserLog { Id= 1, Date = new DateTime(2012,1,1), Username = "cburgdorf"},
new UserLog { Id= 2, Date = new DateTime(2012,1,1), Username = "cburgdorf"},
new UserLog { Id= 3, Date = new DateTime(2012,1,1), Username = "cburgdorf"},
new UserLog { Id= 4, Date = new DateTime(2012,1,1), Username = "Mister Foo"},
new UserLog { Id= 5, Date = new DateTime(2012,1,1), Username = "Mister Foo"},
new UserLog { Id= 6, Date = new DateTime(2012,1,2), Username = "Mister Bar"},
new UserLog { Id= 7, Date = new DateTime(2012,1,2), Username = "Mister Bar"},
new UserLog { Id= 8, Date = new DateTime(2012,1,2), Username = "cburgdorf"},
new UserLog { Id= 9, Date = new DateTime(2012,1,2), Username = "Mister Foo"},
new UserLog { Id= 10, Date = new DateTime(2012,1,2), Username = "Mister Foo"},
new UserLog { Id= 11, Date = new DateTime(2012,1,2), Username = "Mister Foo"},
new UserLog { Id= 12, Date = new DateTime(2012,1,2), Username = "Mister Bar"}
};
logs
.OrderByDescending (l => l.Date)
.GroupBy (log => log.Date)
.Select (log => log
.GroupBy (l => l.Username)
.Select (l => new
{
Count = l.Count(),
Value = l.FirstOrDefault(),
})
.OrderBy (l => l.Count).Last())
.Select (log => new
{
Date = log.Value.Date,
Count = log.Count,
Username = log.Value.Username
})
.Take(10)
.Dump();
//In LINQPad use Dump() to see the results:
/*
logs
.OrderByDescending (l => l.Date)
.GroupBy (log => log.Date)
.Select (log => log
.GroupBy (l => l.Username)
.Select (l => new
{
Count = l.Count(),
Value = l.FirstOrDefault(),
})
.OrderBy (l => l.Count).Last())
.Select (log => new
{
Date = log.Value.Date,
Count = log.Count,
Username = log.Value.Username
})
.Take(10)
.Dump();
*/
}
class UserLog
{
public int Id {get;set;}
public DateTime Date {get;set;}
public string Username {get;set;}
}
The result is:
02.01.2012 00:00:00 | 3 | Mister Foo
01.01.2012 00:00:00 | 3 | cburgdorf
這個問題也被標記爲[tag：sql]，所以你可能不得不考慮在回答時他是否使用LINQ to SQL。你在這裏使用了LINQ to Objects，並不是所有的方法都被支持。幸運的是，我認爲你在這裏是安全的，因爲你使用的所有方法都會被支持。 –
絕對如此。我不確定這是否會在使用EntityFramework或LinqToEntities時轉換爲SQL。如果是這樣，它將如何執行？很難說真的，也取決於後端。對於Oracle後端，我遇到了很多「bla bla not supported exceptions」，例如，在SQL Server上，相同的查詢翻譯得很好。有時候這是一種痛苦... – Christoph
這應該工作。這將選擇最近10天內的最高用戶。
var query =
(from userLog in data.UserLogs
group userLog.UserName by userLog.Date.Date into usersPerDate
orderby usersPerDate.Key descending
let topUsers =
from user in usersPerDate
group 1 by user into g
let count = g.Count()
orderby count descending
select new
{
UserName = g.Key,
Count = count,
}
select topUsers.First()).Take(10);
謝謝你的回答 – Sam
你能澄清：是的'Date'列*日期*或*日期和時間*？ –
它是日期時間。 – Sam
主要分組可能只是「通過entry.Date.Date」組，然後 - 真正有問題的是每天*最活躍的用戶*在同一時間*。坦率地說，我認爲我會下降到TSQL - 這不是一個微不足道的查詢。 –