Module 9
Designing 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 permitted
CREATE AGGREGATE CREATE RULE
CREATE DEFAULT CREATE SCHEMA
CREATE or ALTER FUNCTION CREATE or ALTER TRIGGER
CREATE or ALTER PROCEDURE CREATE or ALTER VIEW
SET PARSEONLY SET SHOWPLAN_ALL
SET SHOWPLAN_TEXT SET SHOWPLAN_XML
USE databasename
Demonstration 1A: Working with System Stored Procedures and Extended Stored Procedures
In 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 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; 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 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;
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 proceduresüü
Keep consistent SET optionsüü
Apply consistent naming conventions (and no sp_ prefix)üü
Use @@nestlevel to see current nesting level (32 max)üü
Keep one procedure per tasküü
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;
CREATE PROCEDURE HumanResources.EmployeeListWITH ENCRYPTIONAS SELECT EmployeeID, LastName, FirstNameFROM HumanResources.Employee;
Use WITH ENCRYPTION on ALTER PROC to retain encryption
Demonstration 2A: Stored Procedures
In 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;
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;
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 Parameters
In 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)
Sales.SalesOrderHeader(Owner: John)
Ted(No permissions)
Ted(No permissions)
Procedure(Owner: Pat)Procedure
(Owner: Pat)
GetOrderCountByDueDateGetOrderCountByDueDate
Ted(EXECUTE permission)
Ted(EXECUTE permission) PatPat
Pat(SELECT permission)
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 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;
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 Impersonationüü
Provides access to modules via impersonationüü
Can be used to impersonate server-level principals or logins via the EXECUTE AS LOGIN statement
üü
Can be used to impersonate database level principals or users via the EXECUTE AS USER statementüü
CREATE PROCEDURE Sales.GetOrders WITH EXECUTE AS {CALLER | SELF | OWNER | ‘user_name’ }AS…
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 Context
In 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-SQL
User name AdventureWorks\Administrator
Password Pa$$w0rd
Lab Scenario
You 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