Scaler Function in Where Clause Really Slow? How to use Cross Apply Instead? - where-clause

Question

I have some data, some of it was imported with different separators such as * - . or a space...some of it was removed on import, some was not. Some of the external values being compared to it has the same issue. So we remove all separators and compare that way, I don't want to just update the columns yet as the data isn't "mine".
So since I see this over and over in the code I am moving to stored procedures, I wrote a stored function to do it for me.
ALTER FUNCTION [dbo].[fn_AccountNumber_Format2]
(#parAcctNum NVARCHAR(50))
RETURNS NVARCHAR(50)
AS
BEGIN
SET #parAcctNum = REPLACE(REPLACE(REPLACE(REPLACE(#parAcctNum, '.', ''), '*', ''), '-', ''), ' ', '');
RETURN #parAcctNum
END
Normally the queries looked something like this and it takes less than a second to run on a few millions rows :
SELECT name1, accountID FROM tblAccounts WHERE (Replace(Replace(Replace(accountnumber, '.', ''), '*', ''), '-', '') = Replace(Replace(Replace('123-456-789', '.', ''), '*', ''), '-', ''));
So my first attempt with it like this takes 24 seconds to excecute:
SELECT name1, accountID FROM tblAccounts WHERE (dbo.fn_AccountNumber_Format2 ([accountnumber])) = Replace(Replace(Replace('123-456-789', '.', ''), '*', ''), '-', '');
This one 43 seconds:
SELECT name1, accountID FROM tblAccounts WHERE (dbo.fn_AccountNumber_Format2(accountnumber)) = (dbo.fn_AccountNumber_Format2 ('123-456-789'));
So the drastic slow down came as a complete shock to me as I expected the user defined function to run just the same as the system function REPLACE... After some research on stackexchange and google it seems that using Cross Apply and creating a table with the function may be a better solution but I have no idea how that works, can anyone help me with that?

Answer 1

Inline Function
CREATE FUNCTION [dbo].[uspAccountNumber_Format3]
(
#parAcctNum NVARCHAR(50))
RETURNS TABLE
AS
RETURN
(
SELECT REPLACE(REPLACE(REPLACE(REPLACE(#parAcctNum, '.', ''), '*', ''),'-', ''), ' ', '') AS AccountNumber
)
Usage
SELECT name1 ,
accountID
FROM tblAccounts
CROSS APPLY dbo.uspAccountNumber_Format3(accountnumber) AS a
CROSS APPLY dbo.uspAccountNumber_Format3('123-456-789') AS b
WHERE a.AccountNumber = b.AccountNumber