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

The default is the first place we start to see any real divergence from variables. Where variables are
always initialized to a NULL value, parameters are not. Indeed, if you don’t supply a default value, then
the parameter is assumed to be required, and a beginning value must be supplied when the sproc is
called.
So, for example, let’s try a slightly different version of our previous sproc. This time, we’ll be supplying
name information from the Person.Person table and accepting a filter for the last name:
USE AdventureWorks2008;
GO
CREATE PROC spEmployeeByName
@LastName nvarchar(50)
AS
SELECT p.LastName, p.FirstName, e.JobTitle, e.HireDate
FROM Person.Person p
JOIN HumanResources.Employee e
ON p. BusinessEntityID = e.BusinessEntityID
WHERE p.LastName LIKE @LastName + ‘%’;
Try this sproc supplying the required default:
EXEC spEmployeeByName ‘Dobney’;
And you get a very short list back (indeed, just one employee):
LastName FirstName JobTitle HireDate
------------ ------------ ----------------------------- ----------
Dobney JoLynn Production Supervisor - WC60 1998-01-26
Be careful using wildcard matches, such as the LIKE statement used in the preceding
code. This particular example would likely perform OK because the wildcard is at the
end. Keep in mind that wildcards used at the beginning of a search effectively eliminate
the opportunity for SQL Server to use an index since any starting character is
potentially a match.
Now check what happens if we don’t supply the default:
EXEC spEmployeeByName;
SQL Server wastes no time in informing us of the error of our ways:
Msg 201, Level 16, State 4, Procedure spEmployeeByName, Line 0
Procedure or Function ‘spEmployeeByName’ expects parameter ‘@LastName’, which was
not supplied.
Because no default was provided, the parameter is assumed to be required.
Chapter 12: Stored Procedures
371