6232 b 04
TRANSCRIPT
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)
EmployeeID LastName FirstName Title BirthDate …
287 Mensa-Annan Tete Mr. 3/2/1984 …
288 Abbas Syed Mr. 4/5/1976 …
289 Valdez Rachel NULL 9/8/1973 …
EmployeeList (view)
EmployeeID LastName FirstName
287 Mensa-Annan Tete
288 Abbas Syed
289 Valdez Rachel
• 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.EmployeeListASSELECT EmployeeID, LastName, FirstNameFROM 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.EmployeeListASSELECT EmployeeID, LastName, FirstName, PostalCodeFROM HumanResources.Employee;
Ownership Chains and Views
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
OBJECT_DEFINITION()Function that returns definition of non-encrypted views
sys.sql_expression_dependenciesObjects (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.EmployeeListWITH ENCRYPTIONASSELECT EmployeeID, LastName, FirstNameFROM 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.SaleSQLServerNorth.Sales.Sale
CREATE VIEW Sales.AllSales ASSELECT * FROMSQLServerNorth.Sales.SaleUNION ALLSELECT *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 WebStockViews
• 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
Virtual machine 623XB-MIA-SQL
User name AdventureWorks\Administrator
Password Pa$$w0rd
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 AvailableModelsview. 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