ViewsSimilar to an Access query

Predefined SELECT statementAt most basic level specifies which columns

and rows to returnProvides a virtual table

SELECT * FROM Customers represents rows and columns but isn’t for storing data

Reasons for ViewsReduce database complexity‘Hide’ sensitive dataImprove query performance

Reduce ComplexityProvide access to data from multiple tables

Normalization doesn’t get in the wayLimit number of columns returned

Instead of returning all columns just return ones commonly used

Hiding DataProvide only columns that are appropriateProvide only rows that are appropriateCan have multiple views on one table with

different fields and criteria for different user groups

Can also hide table and database organization

Ease of UseCan provide access to current information

List only students who are currently enrolled in a course

Can organize data for common reportsList students with assignments for a section

View OptionsEncryption prevents viewing the SQL

statementSchema binding ties the view to objects it

depends onCan’t drop a table – or column – that’s

referenced in a bound viewCan sort results

Requires use of TOP optionCan also use ORDER BY in SELECT where

view is used

PerformanceBy default views run just as a query

processed from command lineAdds second step to execution:

select from view execute view itself

Can add an index to speed execution

Indexed ViewsSpeeds up execution of query, but has rules:

View must be schema-boundView can’t reference other views (only tables &

functions)Two-part names required, and must be same

owner as view (dbo.Students)

Indexed Views (cont.)View and source tables must be in same

databaseFunctions used must be deterministicANSI_NULLS and QUOTED_IDENTIFIERS

must be on when view and source tables created ANSI_NULL – Set to on requires use of IS to

compare to NULL QUOTED_IDENTIFIERS – Set to on indicates that

double quotes identify object names

DeterministicAn indexed view must be deterministic

Result of calculation is the same with same inputs

DateAdd is deterministicGetDate is non-deterministic

Places to Consider An IndexJoins and aggregations of large tables Repeated patterns of queries (common

WHERE clause) Repeated aggregations on the same or

overlapping sets of columns Repeated joins of the same tables on the

same keys

Indexes’ DownsideHave another list that must be maintained

when data changesCan’t reference other viewsTables must be in same databaseCannot sort view in definition

Can use ORDER BY when view referenced in SELECT

Unique clustered index must be created before any other indexes can be created

Updateable ViewsCan update base tables through a view. To have an updateable view,

Can’t include a DISTINCT or TOP clause.Field list can’t include an aggregate function.Field list can’t include a calculated value.Can’t include a GROUP BY or HAVING clause.Can’t include the UNION operator.

Updating rows using a viewUse the UPDATE statement to update a table

through a viewUse the view name in the UPDATE clauseThe view must be updatable (prior slide)The UPDATE statement can’t update data in

more than one table.

WITH CHECKIf WITH CHECK is used when the view is

created, trying to change a row such that it wouldn’t be included in the view result will result in an error.If a view only returns rows where city =

‘Olympia’, and city is changed to ‘Lacey’ an error occurs