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

Chapter 13: User-Defined Functions
Even using a table valued output parameter, you still need to make at least one additional step before
using the results in a query.
With a UDF, however, you can pass parameters in, but not out. Instead, the concept of output parameters
has been replaced with a much more robust return value. As with system functions, you can return a scalar
value — what’s particularly nice, however, is that this value is not limited to just the integer data type
as it would be for a sproc. Instead, you can return most SQL Server data types (more on this in the next
section).
As they like to say in late-night television commercials: “But wait! There’s more!” The “more” is that you
are actually not just limited to returning scalar values — you can also return tables. This is wildly powerful,
and we’ll look into this fully later in the chapter.
So, to summarize, we have two types of UDFs:
❑ Those that return a scalar value
❑ Those that return a table
Let’s take a look at the general syntax for creating a UDF:
CREATE FUNCTION [.]
( [ [AS] [.] [ =
[READONLY]]
[ ,...n ] ] )
RETURNS {|TABLE [()]}
[ WITH [ENCRYPTION]|[SCHEMABINDING]|
[ RETURNS NULL ON NULL INPUT | CALLED ON NULL INPUT ] | [EXECUTE AS {
CALLER|SELF|OWNER|} ]
]
[AS] { EXTERNAL NAME |
BEGIN
[]
{RETURN |RETURN ()}
END }[;]
This is kind of a tough one to explain because parts of the optional syntax are dependent on the choices
you make elsewhere in your CREATE statement. The big issues here are whether you are returning a
scalar data type or a table and whether you’re doing a T-SQL-based function or doing something utilizing
the CLR and .NET. Let’s look at each type individually.
UDFs Retur ning a Scalar V alue
412
This type of UDF is probably the most like what you might expect a function to be. Much like most of
SQL Server’s own built-in functions, they will return a scalar value to the calling script or procedure;
functions such as GETDATE() or USER() return scalar values.
As I indicated earlier, one of the truly great things about a UDF is that you are not limited to an integer
for a return value — instead, it can be of any valid SQL Server data type (including user-defined data