User Defined Function Intro

				Brief introduction to User Defined Functions

What is a user defined function?

	User defined functions are very simular to stored procedures.
	Rather then returning recordsets, they can only return variables.
	They are also limited to the types of variables you may return.
	For example - text, ntext, and image datatypes can not be returned.

Ok, so how would it benefit me?

	The magic of user defined functions is that you can use them in
	SELECT, UPDATE, DELETE, & SET statments. You can use them in triggers
	and other places. Somehow I get the idea that you are scratching your
	head still asking "What is it?". Let me show you a small example.


	
	SELECT UserID, dbo.FullName(UserID) FROM Users
	


	In this example, the function is called FullName.
	As you may have guessed, the function returns the full name
	of the user within the record.

How would I make a function?

	Glad you asked. When you open your database in the SQL Server
	Enterprise Manager, one of the nodes available will state "User
	Defined Functions". I usually do a right-mouse-click and click on

	New User Defined Function ...

	A default template may appear ...

	
		CREATE FUNCTION [OWNER].[FUNCTION NAME] (PARAMETER LIST) 

		RETURNS (return_type_spec) AS

		BEGIN 

		(FUNCTION BODY) 

		END
	

	This function is not valid nor helpful. It doesn't even pass when you click on
	the button "Check Syntax". 
	It took me a good amount of
	research along with trial & error before I got the gist of what was going
	on.

So how about a demonstration?

	Right O! Lets go with creating the "FullName" function.
	Here is my code:


CREATE FUNCTION [dbo].[FullName] (@UserID int)
RETURNS varchar(255)
AS 
BEGIN 
	Select
		@FullName = @FirstName + ' ' + @LastName
	FROM
		[Users]
	WHERE
		[UserID] = @UserID
	Return(@FullName)
END


	So first, you can see that the parameter list has been changed to pass
	a Integer variable called UserID. You can add more parameters as long as
	you seperate them with a comma.


	Next we see that the return type, and the parethesies around it has been
	replaced with a datatype "varchar(255)". You are not limited to varchars alone.
	Just about any type of datatype is available except cursors, records, and
	datatypes with pointers (text, ntext, image, etc.).


	If you look at the very bottom, you will see "Return(@FullName)". This
	is where we return the results to the query that called the function.


	And within the BEGIN and END statements, we have the body of the function.

Closing Comments

	The demonstration here is very inefficient. It is here only as a reference
	to get you started. Defining your own functions allows more complex business
	logic & formatting to be possible. Consider the ability to pass in a piece of
	text of 4000 characters long and inserting HTML links on specific keywords.
	Another idea would be to perform lookups on multiple tables and return a value
	that best suites your query.