Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 13: User-Defined Functions
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Look back through the list of requirements for a deterministic function and see if you can figure out why
this one doesn’t meet the grade.
When I was working on this example, I got one of those not so nice little reminders about how it’s the
little things that get you. You see, I was certain this function should be deterministic, and, of course, it
wasn’t. After too many nights writing until the morning hours, I completely missed the obvious —
SCHEMABINDING.
Fortunately, we can fix the only problem this one has. All we need to do is add the WITH SCHEMABINDING
option to our function, and we’ll see better results:
ALTER FUNCTION dbo.DayOnly(@Date date)
RETURNS date
WITH SCHEMABINDING
AS
BEGIN
RETURN @Date;
END
Now, we just rerun our OBJECTPROPERTY query:
-----------
1
(1 row(s) affected)
And voilà — a deterministic function!
We can compare this, however, with our AveragePrice function that we built in the AdventureWorks2008
database. It looked something like this:
CREATE FUNCTION dbo.AveragePrice()
RETURNS money
WITH SCHEMABINDING
AS
BEGIN
RETURN (SELECT AVG(ListPrice) FROM Production.Product);
END
GO
CREATE FUNCTION dbo.PriceDifference(@Price money)
RETURNS money
AS
BEGIN
RETURN @Price - dbo.AveragePrice();
END
In this function we used schema-binding right from the beginning, so let’s look at our OBJECTPROPERTY:
USE AdventureWorks2008;
SELECT OBJECTPROPERTY(OBJECT_ID(‘AveragePrice’), ‘IsDeterministic’);