I agree that it is parameter sniffing, and adding the declare etc to the query makes it run faster.

My next question is, how do I do this in a view...

Here is the general structure of my function:

ALTER FUNCTION [dbo].[fnInventory] (@ClosingDate DateTime )

RETURNS TABLE

AS

RETURN

(

SELECT

*

FROM

InventoryCostUnit WITH (NOLOCK)

LEFT JOIN

(

SELECT *

FROM BIMovement

WHERE TransactionDateTime...