Module 9Designing and

Implementing Stored Procedures

Module Overview• Introduction to Stored Procedures• Working with Stored Procedures• Implementing Parameterized Stored Procedures• Controlling Execution Context

Lesson 1: Introduction to Stored Procedures• What is a Stored Procedure?• Benefits of Stored Procedures• Working with System Stored Procedures• Statements not Permitted• Demonstration 1A: Working with System Stored Procedures

and Extended Stored Procedures

What is a Stored Procedure?• When applications interact with SQL Server, there are two

basic ways to execute T-SQL code: Every statement can be issued directly by the application Groups of statements can be stored on the server as stored

procedures and given a name. The application then calls the procedures by name.

• Stored procedures Are similar to procedures or methods in other languages Can have input parameters Can have output parameters Can return sets of rows Are executed by the EXECUTE T-SQL statement Can be created in managed code or T-SQL

Benefits of Stored Procedures• Can enhance the security of an application as they are a

security boundary Users can be given permission to execute a stored procedure

without permission to the objects it accesses• Allow for modular programming

Create once, call many times and from many applications• Allow for delayed binding of objects

Can create a stored procedure that references a database object that doesn't exist yet.

Can avoid the need for ordering in object creation• Can improve performance

Single statement requested across the network can execute hundreds of lines of T-SQL code

Better opportunities for execution plan reuse

Working with System Stored Procedures• Large number of system stored procedures is supplied with

SQL Server• Two basic types of system stored procedure:

System Stored Procedures – typically used for administrative purposes to either configure servers, databases or objects or to view information about them.

System Extended Stored Procedures – extend the functionality of SQL Server.

• Key difference is how they are coded: System Stored Procedures are T-SQL code in the master

database System Extended Stored Procedures are references to DLLs

Statements not Permitted• Not all T-SQL statements are permitted in stored

procedures.• In particular, the following list are not permitted:

Statements not permittedCREATE AGGREGATE CREATE RULECREATE DEFAULT CREATE SCHEMACREATE or ALTER FUNCTION CREATE or ALTER TRIGGERCREATE or ALTER PROCEDURE CREATE or ALTER VIEWSET PARSEONLY SET SHOWPLAN_ALLSET SHOWPLAN_TEXT SET SHOWPLAN_XMLUSE databasename

Demonstration 1A: Working with System Stored Procedures and Extended Stored ProceduresIn this demonstration you will see:• How to execute system stored procedures• How to execute system extended stored procedures

Lesson 2: Working with Stored Procedures• Creating a Stored Procedure• Executing Stored Procedures• Altering a Stored Procedure• Dropping a Stored Procedure• Stored Procedure Dependencies• Guidelines for Creating Stored Procedures• Obfuscating Stored Procedure Definitions• Demonstration 2A: Stored Procedures

Creating a Stored Procedure

CREATE PROCEDURE Sales.GetSalespersonNamesAS SELECT s.BusinessEntityID, p.LastName, p.FirstNameFROM Sales.Salesperson AS sINNER JOIN Person.Person AS pON s.BusinessEntityID = p.BusinessEntityIDWHERE s.TerritoryID IS NOT NULLORDER BY s.BusinessEntityID;

• CREATE PROCEDURE is used to create new stored procedures• The procedure must not already exist, otherwise ALTER must be

used or the procedure dropped first• CREATE PROCEDURE must be the only statement in a batch

Executing Stored Procedures

EXEC Sales.GetSalespersonNames;

• EXECUTE statement: Used to execute stored procedures and other objects such as

dynamic SQL statements stored in a string Can execute system stored procedures (sp_ prefix) from within

the master database without having to refer to that database.• Use two part naming when executing local stored procedures

within a database. Otherwise, SQL Server searches for the procedure: In the sys schema of the current database In the caller's default schema in the current database In the dbo schema in the current database

Altering a Stored Procedure

ALTER PROCEDURE Sales.GetSalespersonNamesAS SELECT s.BusinessEntityID, p.LastName, p.FirstNameFROM Sales.Salesperson AS sINNER JOIN Person.Person AS pON s.BusinessEntityID = p.BusinessEntityIDWHERE s.TerritoryID IS NOT NULLAND s.SalesQuota IS NOT NULLORDER BY s.BusinessEntityID;

• ALTER PROCEDURE Used to replace a stored procedure Retains the existing permissions on the procedure

Dropping a Stored Procedure

SELECT SCHEMA_NAME(schema_id) AS SchemaName, name AS ProcedureNameFROM sys.procedures;GO

DROP PROCEDURE Sales.GetSalespersonNames;

• DROP PROCEDURE removes one or more stored procedures from the current database

• Find the list of existing procedures in the current database by querying the sys.procedures system view

• Use sp_dropextendedproc to drop Extended Stored Procedures

Stored Procedure Dependencies• New system views replace the use of sp_depends• sys.sql_expression_dependencies

Contains one row per by-name dependency on a user-defined entities in the current database

• sys.dm_sql_referenced_entities Contains one row for each entity referenced by another entity

• sys.dm_sql_referencing_entities Contains one row for each entity referencing another entity

Guidelines for Creating Stored Procedures

Qualify names inside of stored proceduresü

Keep consistent SET optionsü

Apply consistent naming conventions (and no sp_ prefix)ü

Use @@nestlevel to see current nesting level (32 max)ü

Keep one procedure per taskü

Obfuscating Stored Procedure Definitions

• WITH ENCRYPTION clause Encrypts stored procedure definition stored in SQL Server Protects stored procedure creation logic to a limited extent Is generally not recommended

CREATE PROCEDURE HumanResources.EmployeeListWITH ENCRYPTIONAS SELECT EmployeeID, LastName, FirstNameFROM HumanResources.Employee;

Use WITH ENCRYPTION on ALTER PROC to retain encryption

Demonstration 2A: Stored ProceduresIn this demonstration, you will see:• How to create a stored procedure• How to execute a stored procedure• How to create a stored procedure that returns multiple

rowsets• How to alter a stored procedure• How to view the list of stored procedures

Lesson 3: Implementing Parameterized Stored Procedures • Working with Parameterized Stored Procedures• Using Input Parameters• Using Output Parameters• Parameter Sniffing and Performance• Demonstration 3A: Stored Procedure Parameters

Working with Parameterized Stored Procedures

Input parameters

Output parameters

Return values

Parameterized stored procedures contain 3 major components:

Using Input Parameters

CREATE PROCEDURE Sales.OrdersByDueDateAndStatus@DueDate datetime, @Status tinyint = 5AS SELECT soh.SalesOrderID,soh.OrderDate,soh.CustomerIDFROM Sales.SalesOrderHeader AS sohWHERE soh.DueDate = @DueDateAND soh.[Status] = @StatusORDER BY soh.SalesOrderID;GOEXEC Sales.OrdersByDueDateAndStatus '20050713',5;EXEC Sales.OrdersByDueDateAndStatus '20050713';EXEC Sales.OrdersByDueDateAndStatus @DueDate = '20050713', @Status = 5;

• Parameters Have @ prefix, data type, can have a default value Can be passed in order or can be passed by name (but no

combination of these is permitted in one statement)• Validate input parameters early in stored procedure code

Using Output Parameters

CREATE PROC Sales.GetOrderCountByDueDate@DueDate datetime, @OrderCount int OUTPUTAS SELECT @OrderCount = COUNT(1) FROM Sales.SalesOrderHeader AS soh WHERE soh.DueDate = @DueDate;GODECLARE @DueDate datetime = '20050713';DECLARE @OrderCount int;EXEC Sales.GetOrderCountByDueDate @DueDate, @OrderCount OUTPUT;SELECT @OrderCount;

• OUTPUT must be specified: When declaring the parameter When executing the stored procedure

Parameter Sniffing and Performance

• Query plan generated for a stored procedure is mostly reused the next time the stored procedure is executed

• In general, this is very desirable behavior• Some stored procedures need to have very different query plans

for different sets of parameters before they will perform optimally Problem is commonly called a "parameter sniffing" problem

• Options for resolving CREATE PROC xyz WITH RECOMPILE sp_recompile 'xyz' EXEC WITH RECOMPILE OPTION (OPTIMIZE FOR)

Demonstration 3A: Stored Procedure ParametersIn this demonstration you will see:• How to create a stored procedure with parameters• How to alter a stored procedure with parameters to correct

a common stored procedure bug

Lesson 4: Controlling Execution Context • Controlling Execution Context• The EXECUTE AS Clause• Viewing Execution Context• Demonstration 4A: Viewing Execution Context

Controlling Execution Context

Sales.SalesOrderHeader(Owner: John)

Ted(No permissions)

Procedure(Owner: Pat)

GetOrderCountByDueDate

Ted(EXECUTE permission) Pat

Pat(SELECT permission)

CREATE PROC Sales.GetOrderCountByDueDate@DueDate datetime, @OrderCount int OUTPUTAS SELECT @OrderCount = COUNT(1) FROM Sales.SalesOrderHeader AS soh WHERE soh.DueDate = @DueDate;

CREATE PROC Sales.GetOrderCountByDueDate@DueDate datetime, @OrderCount int OUTPUTWITH EXECUTE AS 'Pat'AS SELECT @OrderCount = COUNT(1) FROM Sales.SalesOrderHeader AS soh WHERE soh.DueDate = @DueDate;

The EXECUTE AS Clause

Enables Impersonationü Provides access to modules via impersonationü Can be used to impersonate server-level principals or logins via the EXECUTE AS LOGIN statement

ü

Can be used to impersonate database level principals or users via the EXECUTE AS USER statementü

CREATE PROCEDURE Sales.GetOrders WITH EXECUTE AS {CALLER | SELF | OWNER | ‘user_name’ }AS…

Viewing Execution Context• Details of the current security context can be viewed

programmatically sys.login_token shows the login-related details

sys.user_token shows the user-related details

Demonstration 4A: Viewing Execution ContextIn this demonstration you will see:• How to view details of execution context• How to change execution context for a session• How to use the WITH EXECUTE AS clause in a stored

procedure

Lab 9: Designing and Implementing Stored Procedures• Exercise 1: Create stored procedures• Exercise 2: Create a parameterized stored procedure• Challenge Exercise 3: Alter the execution context of stored

procedures (Only if time permits)

Logon information

Estimated time: 45 minutes

Virtual machine 623XB-MIA-SQLUser name AdventureWorks\AdministratorPassword Pa$$w0rd

Lab ScenarioYou need to create a set of stored procedures to support a new reporting application. The procedures will be created within a new Reports schema.

Lab Review• When is the OUTPUT keyword needed for output

parameters in working with stored procedures?• What does the sys.login_token view show?

Module Review and Takeaways• Review Questions• Best Practices