Using a UDF multiple times in a Sproc - tsql

Question

I have a SQL 2k5 sproc I'm working with.
I need to reference a UDF to calculate price based on a few variables and the users permissions. I originally tried this, but it didn't work because I wasn't referencing a field...
SELECT dbo.f_GetPrice(model,userid,authType) 'YourPrice', name, description
FROM tblRL_Products
WHERE 'YourPrice' Between #fromPrice AND #toPrice
OR 'YourPrice' IS NULL
So I modified this to
SELECT dbo.f_GetPrice(model,userid,authType) 'YourPrice', name, description
FROM tblRL_Products
WHERE dbo.f_GetPrice(model,userid,authType) Between #fromPrice AND #toPrice
OR dbo.f_GetPrice(model,userid,authType) IS NULL
When SQL executes this sproc, is it running the function 3X's for each record or does it run it the one time and use the values in the other two places per row.
Is there a more efficient way of doing this?
Edit
This is the Scalar UDF. It needs to grab a price based on the type the user is authorized for, then once we have the right price we need to do a calculation on it. This is all stored in the authorization tables. Every user has an authorization for each line of products. So they may have different price types and calculations for each line, returning back dozens or even hundreds of lines in a single search result call.
In the above code I used authType, that was an old call, we don't use that parameter anymore.
ALTER function [dbo].[f_GetPrice]
(
#model uniqueidentifier,
#userID uniqueidentifier
)
returns money
as
begin
Declare #yourPrice money
WITH ProductPrice AS(
SELECT (CASE PriceType
WHEN 'msrp' THEN p.price_msrp
WHEN 'jobber' THEN p.price_jobber
WHEN 'warehouse' THEN p.price_warehouse
WHEN 'margin' THEN p.price_margin
WHEN 'mycost' THEN p.price_mycost
WHEN 'customprice1' THEN p.price_custom1
WHEN 'customprice2' THEN p.price_custom2
WHEN 'customprice3' THEN p.price_custom2
ELSE p.price_msrp
END) as YourPrice, aup.calc, aup.amount
FROM products p
JOIN lines l ON l.lineID=l.lineID
JOIN authorizations a ON l.authlineID=a.authlineID
JOIN authorizationusers au ON a.auID=au.auID
JOIN authorizationuserprices aup ON au.aupID=aup.aupID
WHERE au.userID=#userID AND p.modelID=#model)
SELECT #yourPrice=(CASE calc
WHEN 'amount' THEN YourPrice+amount
WHEN 'percent' THEN YourPrice+(YourPrice*amount/100)
WHEN 'divide' THEN YourPrice/amount
WHEN 'factore' THEN YourPrice*amount
WHEN 'none' THEN YourPrice
ELSE YourPrice
END) FROM ProductPrice
return #yourPrice
END

Answer 1

If you must use a udf for this, then use a subquery and filter outside the subquery:
select YourPrice, name, description
from
(
SELECT dbo.f_GetPrice(model,userid,authType) YourPrice, name, description
FROM tblRL_Products
) d
WHERE YourPrice Between #fromPrice AND #toPrice
OR YourPrice IS NULL
Then you are only calling your udf once instead of 3 times.

Answer 2

Scalar functions are not good, when they have to be applied to a quite number of rows. In this case definitely you can convert your scalar function into table-valued function, which will not be called one time for every row of input data.
create function [dbo].[ft_GetPrice]
(
#model uniqueidentifier,
#userID uniqueidentifier
)
returns table
as return
(
WITH ProductPrice AS (
SELECT (CASE PriceType
WHEN 'msrp' THEN p.price_msrp
WHEN 'jobber' THEN p.price_jobber
WHEN 'warehouse' THEN p.price_warehouse
WHEN 'margin' THEN p.price_margin
WHEN 'mycost' THEN p.price_mycost
WHEN 'customprice1' THEN p.price_custom1
WHEN 'customprice2' THEN p.price_custom2
WHEN 'customprice3' THEN p.price_custom2
ELSE p.price_msrp
END) as YourPrice, aup.calc, aup.amount
FROM products p
JOIN lines l ON l.lineID=l.lineID
JOIN authorizations a ON l.authlineID=a.authlineID
JOIN authorizationusers au ON a.auID=au.auID
JOIN authorizationuserprices aup ON au.aupID=aup.aupID
WHERE au.userID=#userID AND p.modelID=#model
)
SELECT
CASE calc
WHEN 'amount' THEN YourPrice+amount
WHEN 'percent' THEN YourPrice+(YourPrice*amount/100)
WHEN 'divide' THEN YourPrice/amount
WHEN 'factore' THEN YourPrice*amount
WHEN 'none' THEN YourPrice
ELSE YourPrice
END as YourPrice
FROM ProductPrice
)
GO
Which can be used then as:
SELECT fp.YourPrice, name, description
FROM tblRL_Products
outer apply dbo.ft_GetPrice(model, userid, authType) fp
WHERE fp.YourPrice Between #fromPrice AND #toPrice OR fp.YourPrice IS NULL