Module 4 Designing and Implementing Views

Module Overview Introduction to Views Creating and Managing Views Performance Considerations for Views

Lesson 1: Introduction to Views What is a View? Types of Views Advantages of Views Working with System Views Dynamic Management Views Demonstration 1A: System and Dynamic Management Views

What is a View? Employee (table) EmployeeIDLastNameFirstNameTitleBirthDate… 287Mensa-AnnanTeteMr.3/2/1984… 288AbbasSyedMr.4/5/1976… 289ValdezRachelNULL9/8/1973… EmployeeList (view) EmployeeIDLastNameFirstName 287Mensa-AnnanTete 288AbbasSyed 289ValdezRachel A view is a database object referenced like a table A view is like a SELECT query with a name A view is a database object referenced like a table A view is like a SELECT query with a name

Types of Views Standard views  Combine data from one or more base tables into a new virtual table System Views  Provide state information for SQL Server and catalogs Indexed views  View that has been computed and stored. You index a view by creating a unique clustered index on it Partitioned views  Joins horizontally partitioned data from a set of tables across one or more servers

Advantages of Views Mask database complexity Simplify management of user permissions Organize data for export to other applications Focus the data for a user Provide backward compatibility Structure data for reporting applications

Working with System Views There are several types of system views: Catalog Views  Return information used by the SQL Server Database Engine Compatibility Views  Many system tables available in earlier versions are now available as system views Information Schema Views  Provide catalog information as defined in the ISO standard for the INFORMATION_SCHEMA.

Dynamic Management Views Monitor server health Diagnose problems, tune performance Some are implemented as functions, some as views Return server state information Named like sys.dm_*

Demonstration 1A: System and Dynamic Management Views In this demonstration, you will see how to: Query system views Query dynamic management views

Lesson 2: Creating and Managing Views Creating Views Dropping Views Altering Views Ownership Chains and Views Sources of Information about Views Updatable Views Obfuscating Views Definitions Demonstration 2A: Implementing Views

Creating Views Use the CREATE VIEW Transact-SQL statement: Restrictions on creating views:  Cannot nest more than 32 levels deep  Cannot use ORDER BY without TOP CREATE VIEW HumanResources.EmployeeList AS SELECT EmployeeID, LastName, FirstName FROM HumanResources.Employee; CREATE VIEW HumanResources.EmployeeList AS SELECT EmployeeID, LastName, FirstName FROM HumanResources.Employee;

Dropping Views Drop by using the DROP VIEW Transact-SQL statement: Also drops all permissions associated with the view Multiple views can be dropped in a single statement  Comma-delimited list of views DROP VIEW HumanResources.EmployeeList;

Altering Views Alter by using the ALTER VIEW Transact-SQL statement: Replaces the definition of a view Does not alter permissions associated with the view ALTER VIEW HumanResources.EmployeeList AS SELECT EmployeeID, LastName, FirstName, PostalCode FROM HumanResources.Employee; ALTER VIEW HumanResources.EmployeeList AS SELECT EmployeeID, LastName, FirstName, PostalCode FROM HumanResources.Employee;

Ownership Chains and Views

Sources of Information About Views SQL Server Management Studio Transact-SQL SourceInformation Object Explorer List of views in database Access to columns, triggers, indexes, and statistics defined on views View Properties dialog box Properties of individual views SourceInformation sys.views List of views in database OBJECT_DEFINITION() Function that returns definition of non- encrypted views sys.sql_expression_dependencies Objects (including views) that depend on other objects

Updatable Views Views do not maintain a separate copy of data Updates to views modify the base tables Updates are restricted by using the WITH CHECK OPTION Restrictions: Cannot affect more than one base table Cannot modify columns derived from functions or expressions Cannot modify columns affected by GROUP BY, HAVING, or DISTINCT clauses

Obfuscating View Definitions WITH ENCRYPTION clause Encrypts view definition stored in SQL Server Protects view creation logic to a limited extent Generally not recommended CREATE VIEW HumanResources.EmployeeList WITH ENCRYPTION AS SELECT EmployeeID, LastName, FirstName FROM HumanResources.Employee; CREATE VIEW HumanResources.EmployeeList WITH ENCRYPTION AS SELECT EmployeeID, LastName, FirstName FROM HumanResources.Employee; Use WITH ENCRYPTION on ALTER VIEW to retain encryption

Demonstration 2A: Implementing Views In this demonstration, you will see how to: Create a view Query a view Query the definition of a view Use the WITH ENCRYPTION option Drop a view Generate a script for an existing view

Lesson 3: Performance Considerations for Views Views and Dynamic Resolution Nested View Considerations Partitioned Views Demonstration 3A: Views and Performance

Views and Dynamic Resolution Dynamic resolution in view optimization can assist performance SQL Server does not retrieve data that it doesn’t need Single query plan for both query and view Query plans do not show standard views SELECT * needs special consideration in views  Should be avoided

Nested View Considerations Views can provide a convenient layer of abstraction in coding Views can be nested up to 32 levels Nested views can hide code complexity  More difficult to troubleshoot performance issues  More difficult to understand code complexity

Partitioned Views vSales SQLServerSouth.Sales.Sale SQLServerNorth.Sales.Sale CREATE VIEW Sales.AllSales AS SELECT * FROM SQLServerNorth.Sales.Sale UNION ALL SELECT * FROM SQLServerSouth.Sales.Sale; CREATE VIEW Sales.AllSales AS SELECT * FROM SQLServerNorth.Sales.Sale UNION ALL SELECT * FROM SQLServerSouth.Sales.Sale; Joins partitioned data from set of tables across servers

Demonstration 3A: Views and Performance In this demonstration, you will see how: Views are eliminated in query plans Views are expanded and integrated into the outer query before being optimized

Lab 4: Designing and Implementing Views Exercise 1: Design, Implement and Test the WebStock Views Exercise 2: Design and Implement the Contacts View Challenge Exercise 3: Modify the AvailableModels View (only if time permits) Logon information Estimated time: 45 minutes

Lab Scenario A new web-based stock promotion system is being rolled out. Your manager is very concerned about providing access from the web-based system directly to the tables in your database. She has requested you to design some views that the web-based system could connect to instead. Details of organizational contacts are held in a number of tables. The relationship management system being used by the account management team needs to be able to gain access to these contacts. However, they need a single view that comprises all contacts. You need to design, implement and test the required view. Finally, if you have time, a request has been received from the new Marketing team that the catalog description of the product models should be added to the AvailableModels view. They would appreciate you modifying the view to provide this additional column.

Lab Review What considerations are there for views that involve multiple tables? What is required for columns in views that are created from expressions?

Module Review and Takeaways Review Questions Best Practices