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

Chapter 13: User-Defined Functions
CREATE FUNCTION dbo.PriceDifference(@Price money)
RETURNS money
AS
BEGIN
RETURN @Price - dbo.AveragePrice();
END
Notice that it’s completely legal to embed one UDF in another one.
Note that the WITH SCHEMABINDING option works for functions just the way that it did for views — if
a function is built using schema-binding, then any object that function depends on cannot be altered or
dropped without first removing the schema-bound function. In this case, schema-binding wasn’t really
necessary, but I wanted to point out its usage and also prepare this example for something we’re going
to do with it a little later in the chapter.
Now let’s run our query using the new functions instead of the old subquery model:
USE AdventureWorks2008
SELECT Name,
ListPrice,
dbo.AveragePrice() AS Average,
dbo.PriceDifference(ListPrice) AS Difference
FROM Production.Product
WHERE ProductSubCategoryID = 1; -- The Mountain Bikes Sub-cat
This yields us the same results we had with our subquery.
Note that, beyond the readability issue, we also get the added benefit of reuse out of this. For a little
example like this, it probably doesn’t seem like a big deal, but as your functions become more complex,
it can be quite a time saver.
UDFs That Retur n a Table
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User-defined functions in SQL Server are not limited to just returning scalar values. They can return
something far more interesting — tables. Now, while the possible impacts of this are sinking in on you,
I’ll go ahead and add that the table that is returned is, for the most part, usable much as any other table
is. You can perform a JOIN against it and even apply WHERE conditions against the results. It’s very cool
stuff indeed.
To make the change to using a table as a return value is not hard at all — a table is just like any other
SQL Server data type as far as a UDF is concerned. To illustrate this, we’ll build a relatively simple one
to start:
USE AdventureWorks2008
GO
CREATE FUNCTION dbo.fnContactList()
RETURNS TABLE