Adding a Helper SQL Index - sql

Question

I have the following View which seems to work quickly enough but when I look at the Execution Plan, it shows the Top N Sort in the second query taking ~90% due to it being repeated for every row in the first query.
Should I be adding an Index to the Loan table to help the ORDER BY clause?
CREATE VIEW [dbo].[ResourceItemStatus] AS
SELECT
i.ID AS ItemID,
i.ResourceID,
i.DateAdded,
i.LocationID,
i.OwnerID,
i.Barcode,
i.MissingReasonID,
i.DateRemoved,
ll.PatronID,
ll.ID AS LoanID,
ll.IssueDateTime,
ll.DueDate,
ll.ReturnDateTime,
ll.LoanTypeID,
ll.RenewalCount,
ll.DeleteSummary,
ll.ReturnStatusID,
ll.FineID,
(SELECT COUNT(*) FROM Loan WHERE Loan.ItemID = i.ID) AS LoanCount,
(SELECT COUNT(*) FROM Item WHERE Item.DateRemoved IS NULL AND Item.ResourceID = i.ResourceID) AS AvailableItemCount
FROM Item i
OUTER APPLY
(
SELECT TOP 1
l.ID,
l.ItemID,
l.PatronID,
l.IssueDateTime,
l.DueDate,
l.ReturnDateTime,
l.LoanTypeID,
l.RenewalCount,
l.DeleteSummary,
l.ReturnStatusID,
l.FineID
FROM Loan l
WHERE l.ItemID = i.ID
ORDER BY l.IssueDateTime DESC, l.ID DESC
) AS ll

Answer 1

Try Windowed Aggregates instead of Scalar Subqueries/Outer Apply:
SELECT
i.ID AS ItemID,
i.ResourceID,
i.DateAdded,
i.LocationID,
i.OwnerID,
i.Barcode,
i.MissingReasonID,
i.DateRemoved,
ll.PatronID,
ll.ID AS LoanID,
ll.IssueDateTime,
ll.DueDate,
ll.ReturnDateTime,
ll.LoanTypeID,
ll.RenewalCount,
ll.DeleteSummary,
ll.ReturnStatusID,
ll.FineID,
coalesce(ll.LoanCount, 0)
COUNT(case when Item.DateRemoved IS NULL then 1 end)
over (partition by ResourceID) AS AvailableItemCount
FROM Item i
LEFT JOIN
(
SELECT
l.ID,
l.ItemID,
l.PatronID,
l.IssueDateTime,
l.DueDate,
l.ReturnDateTime,
l.LoanTypeID,
l.RenewalCount,
l.DeleteSummary,
l.ReturnStatusID,
l.FineID,
COUNT(*) over (partition by ItemId) AS LoanCount,
row_number()
over (partition by ItemId
order by l.IssueDateTime DESC, l.ID DESC) as rn
FROM Loan l
) as ll
on ll.ItemID = i.ID
and ll.rn = 1