在Linq中使用SQL Server的Row_Number

Question

I have a table with data like

Date         Users
------------------
01/03/2015    25
02/03/2015    28
04/03/2015    36
07/03/2015    45
08/03/2015    47

I had created a table valued function in Sql Server using Row_Number which gave me output like below which I used for further processing

Date         Users      UsersAdded
----------------------------------
01/03/2015    25        0
02/03/2015    28        3
04/03/2015    36        8
07/03/2015    45        9
08/03/2015    47        2

However, I need to do the same thing in Linq now but it does not has the Row_Number function. I had a look at How do I translate a query that uses ROW_NUMBER() into linq? but that is not related to my query.

My query in SQL had Rownum upon the date field and query was

select date, Users, (T1.Users - isnull(T2.Users,0)) as UsersAdded
from tableuser T1 
join tableuser T2 on T1.Rownum = (T2.RowNum +1)

I am new to LINQ so don't even know how to start on this query. Any help would be appreciated.

Answer 1

Use the date column to find the next lowest date by dong a left outer join using from / where .

var ans = from t1 in tableuser from t2 in tableuser.Where(t2 => t2.Date == tableuser.Where(t3 => t3.Date < t1.Date).Max(t3 => t3?.Date)).DefaultIfEmpty()
          select new { t1.Date, t1.Users, UsersAdded = t1.Users - (t2?.Users ?? t1.Users)};

PS I think your example query may have an issue with the first answer row?

Answer 2

Use LINQ to object. Refer the link https://msdn.microsoft.com/en-us/library/bb534869.aspx

It will be achieved like this

 string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" }; var query = fruits.Select((fruit, index) => new { index, str = fruit.Substring(0, index) }); foreach (var obj in query) { Console.WriteLine("{0}", obj); } /* This code produces the following output: {index=0, str=} {index=1, str=b} {index=2, str=ma} {index=3, str=ora} {index=4, str=pass} {index=5, str=grape} */