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Monday, July 21, 2008

SQL Server Stored Procedures

By Mike Chapple

Microsoft SQL Server provides the stored procedure mechanism to simplify the database development process by grouping Transact-SQL statements into manageable blocks.

Structure
Stored procedures are extremely similar to the constructs seen in other programming languages. They accept data in the form of input parameters that are specified at execution time. These input parameters (if implemented) are utilized in the execution of a series of statements that produce some result. This result is returned to the calling environment through the use of a recordset, output parameters and a return code. That may sound like a mouthful, but you'll find that stored procedures are actually quite simple.

Example

Let's take a look at a practical example. Assume we have the table shown at the bottom of this page, named Inventory. This information is updated in real-time and warehouse managers are constantly checking the levels of products stored at their warehouse and available for shipment. In the past, each manager would run queries similar to the following:

SELECT Product, Quantity
FROM Inventory
WHERE Warehouse = 'FL'


This resulted in very inefficient performance at the SQL Server. Each time a warehouse manager executed the query, the database server was forced to recompile the query and execute it from scratch. It also required the warehouse manager to have knowledge of SQL and appropriate permissions to access the table information.

We can simplify this process through the use of a stored procedure. Let's create a procedure called sp_GetInventory that retrieves the inventory levels for a given warehouse. Here's the SQL code:

CREATE PROCEDURE sp_GetInventory
@location varchar(10)
AS
SELECT Product, Quantity
FROM Inventory
WHERE Warehouse = @location


Our Florida warehouse manager can then access inventory levels by issuing the command

EXECUTE sp_GetInventory 'FL'
The New York warehouse manager can use the same stored procedure to access that area's inventory.

EXECUTE sp_GetInventory 'NY'

Granted, this is a simple example, but the benefits of abstraction can be seen here. The warehouse manager does not need to understand SQL or the inner workings of the procedure. From a performance perspective, the stored procedure will work wonders. The SQL Sever creates an execution plan once and then reutilizes it by plugging in the appropriate parameters at execution time.

Now that you've learned the benefits of stored procedures, get out there and use them! Try a few examples and measure the performance enhancements achieved -- you'll be amazed!

Inventory Table

ID Product Warehouse Quantity
142 Green beans NY 100
214 Peas FL 200
825 Corn NY 140
512 Lima beans NY 180
491 Tomatoes FL 80
379 Watermelon FL 85

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