SQL stored Proc sample

Following Stored Proc sample is talen from MSDN

USE Northwind
GO
DROP PROCEDURE OrderSummary
GO
CREATE PROCEDURE OrderSummary @MaxQuantity INT OUTPUT AS
-- SELECT to return a result set summarizing
-- employee sales.
SELECT Ord.EmployeeID, SummSales = SUM(OrDet.UnitPrice * OrDet.Quantity)
FROM Orders AS Ord
     JOIN [Order Details] AS OrDet ON (Ord.OrderID = OrDet.OrderID)
GROUP BY Ord.EmployeeID
ORDER BY Ord.EmployeeID

-- SELECT to fill the output parameter with the
-- maximum quantity from Order Details.
SELECT @MaxQuantity = MAX(Quantity) FROM [Order Details]

-- Return the number of all items ordered.
RETURN (SELECT SUM(Quantity) FROM [Order Details])
GO

-- Test the stored procedure.

-- DECLARE variables to hold the return code
-- and output parameter.
DECLARE @OrderSum INT
DECLARE @LargestOrder INT

-- Execute the procedure, which returns
-- the result set from the first SELECT.
EXEC @OrderSum = OrderSummary @MaxQuantity = @LargestOrder OUTPUT

-- Use the return code and output parameter.
PRINT 'The size of the largest single order was: ' +
                 CONVERT(CHAR(6), @LargestOrder)
PRINT 'The sum of the quantities ordered was: ' +
                 CONVERT(CHAR(6), @OrderSum)
GO

The output from running this sample is:

EmployeeID  SummSales                  
----------- -------------------------- 
1           202,143.71                 
2           177,749.26                 
3           213,051.30                 
4           250,187.45                 
5           75,567.75                  
6           78,198.10                  
7           141,295.99                 
8           133,301.03                 
9           82,964.00                  
The size of the largest single order was: 130 
The sum of the quantities ordered was: 51317