Module 7: Implementing Views

Overview Introduction to Views Creating and Managing Views Optimizing Performance by Using Views

Lesson 1: Introduction to Views What Is a View? Types of Views Advantages of Views

What Is a View? Employee (table) vEmployee (view) EmployeeID LastName FirstName Title … 287 Mensa-Annan Tete Mr. 288 Abbas Syed 289 Valdez Rachel NULL vEmployee (view) LastName FirstName Mensa-Annan Tete Abbas Syed Valdez Rachel

Types of Views Standard views Combine data from one or more base tables (or views) into a new virtual table Indexed views Materialize (persist) the view through the creation of a unique clustered index on the view Partitioned views Join horizontally partitioned data from one or more base tables across one or more servers

Advantages of Views Focus the data for a user Mask database complexity Simplify management of user permissions Improve performance Organize data for export to other applications

Lesson 2: Creating and Managing Views Syntax for Creating Views Demonstration: Creating a View Syntax for Altering and Dropping Views How Ownership Chains Affect Views Sources of Information About Views View Encryption Considerations for Modifying Data in a View Practice: Creating a View

Syntax for Creating Views Use CREATE VIEW Transact-SQL statement: Restrictions: Cannot nest more than 32 levels deep Cannot contain more than 1,024 columns Cannot use COMPUTE, COMPUTE BY, or INTO Cannot use ORDER BY without TOP CREATE VIEW [ schema_name.] view_name [ (column [ ,...n ] ) ] [WITH [ENCRYPTION] [SCHEMABINDING] [VIEW_METADATA] ] AS select_statement [ ; ] [ WITH CHECK OPTION ]

Demonstration: Creating a View In this demonstration, you will see how to: Create a view Query a view Generate a script for a view

Syntax for Altering and Dropping Views Alter by using the ALTER VIEW Transact-SQL statement: Drop by using the DROP VIEW Transact-SQL statement: ALTER VIEW [ schema_name.]view_name [ (column [ ,...n ] ) ] [WITH [ENCRYPTION] [SCHEMABINDING] [VIEW_METADATA] ] AS select_statement [ ; ] [ WITH CHECK OPTION ] DROP VIEW [ schema_name.]view_name [ ...,n ] [ ; ]

How Ownership Chains Affect Views 2 View Owner: Mary Access view 1 User: John Dependency 3 View Owner: Mary Dependency 4 Table Owner: Tim

Sources of Information About Views SQL Server Management Studio Transact-SQL Source Information 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 Source Information sys.views List of views in database sp_helptext Definition of non-encrypted views sys.sql_dependencies Objects (including views) that depend on other objects

View Encryption Use the WITH ENCRYPTION option on CREATE VIEW Transact-SQL statement Encrypts view definition in sys.syscomments table Protects view creation logic CREATE VIEW [HumanResources].[vEmployee] WITH ENCRYPTION AS SELECT e.[EmployeeID],c.[Title],c.[FirstName],c.[MiddleName] ,c.[LastName],c.[Suffix],e.[Title] AS [JobTitle] ,c.[Phone],c.[EmailAddress] FROM [HumanResources].[Employee] e INNER JOIN [Person].[Contact] c ON c.[ContactID] = e.[ContactID] Use WITH ENCRYPTION on ALTER VIEW statements to retain encryption

Considerations for Modifying Data in a View Views do not maintain a separate copy of data (indexed views are an exception) Updates to views modify base tables Restrictions: Cannot affect more than one base table Cannot modify columns derived from aggregate functions or calculations Cannot modify columns affected by GROUP BY, HAVING, or DISTINCT clauses Updates to views are restricted by using the WITH CHECK OPTION

Practice: Creating a View In this practice, you will create a view

Lesson 3: Optimizing Performance by Using Views Performance Considerations for Views What Is an Indexed View? What Is a Partitioned View?

Performance Considerations for Views Views introduce performance overhead because views are resolved dynamically Nested views introduce risk of performance problems Review definition of unencrypted nested views Use SQL Server Profiler to review performance Indexed views and partitioned views can improve performance

What Is an Indexed View? A view with a unique clustered index Materializes view, improving performance Allows query optimizer to use view in query resolution Use when: Performance gains outweigh maintenance overhead Underlying data is modified infrequently Queries perform a significant number of joins and aggregations CREATE UNIQUE CLUSTERED INDEX [IX_vStateProvinceCountryRegion] ON [Person].[vStateProvinceCountryRegion] ( [StateProvinceID] ASC, [CountryRegionCode] ASC)

What Is a Partitioned View? Joins horizontally partitioned data from a set of tables across one or more servers SQLServerNorth.Sales.Sale SQLServerSouth.Sales.Sale CREATE VIEW vSales AS SELECT * FROM SQLServerNorth.Sales.Sale UNION ALL SELECT * FROM SQLServerSouth.Sales.Sale vSales

Lab: Implementing Views Exercise 1: Creating Views Exercise 2: Creating Indexed Views Exercise 3: Creating Partitioned Views