Stored procedures are executable server-side routines. They give you great power and performance benefits if used wisely. Unlike user-defined functions (UDFs), stored procedures are allowed to have side effects. That is, they are allowed to change data in tables, and even the schema of objects. Stored procedures can be used as a security layer. You can control access to objects by granting execution permissions on stored procedures and not to underlying objects. You can perform input validation in stored procedures, and you can use stored procedures to allow activities only if they make sense as a whole unit, as opposed to allowing users to perform activities directly against objects.

Stored procedures also give you the benefits of encapsulation; if you need to change the implementation of a stored procedure because you developed a more efficient way to achieve a task, you can issue an ALTER PROCEDURE statement. As long as the procedure’s interface remains the same, the users and the applications are not affected. On the other hand, if you implement your business logic in the client application, the impact of a change can be very painful.

Stored procedures also provide many important performance benefits. By default, a stored procedure will reuse a previously cached execution plan, saving the CPU resources and the time it takes to parse, resolve, and optimize your code. Network traffic is minimized by shortening the code strings that the client submits to Microsoft SQL Server–the client submits only the stored procedure’s name and its arguments, as opposed to the full code. Moreover, all the activity is performed at the server, avoiding multiple roundtrips between the client and the server. The stored procedure will pass only the final result to the client through the network.

This chapter explores stored procedures. It starts with brief coverage of the different types of stored procedures supported by SQL Server 2005 and then delves into details. The chapter covers the stored procedure’s interface, resolution process, compilation, recompilations and execution plan reuse, the EXECUTE AS clause, and the new common language runtime (CLR) stored procedures. You will have a couple of chances in the chapter to practice what you’ve learned by developing stored procedures that serve common practical needs.