McGraw-Hill/Irwin Copyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved.

Chapter 10

Application Development with Views

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Outline

Background Creating views and using views Processing queries that reference views Updatable views Data requirements for hierarchical forms Data requirements for reports

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What is a View? Derived table Behaves like a base table (virtual) with

some restrictions for view usage in modification statements

Stored query

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View Advantages Reduce impact of database definition

changes Simplify database usage Unit of database security Can be a performance penalty on complex

views

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Three Schema Architecture

View 1 View 2 View n

ConceptualSchema

InternalSchema

ExternalLevel

ConceptualLevel

InternalLevel

External toConceptualMappings

Conceptualto InternalMappings

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View Definition Example

Example 1: Create a view consisting of offerings taught by faculty in the MS department.

CREATE VIEW MS_View AS SELECT OfferNo, Course.CourseNo, CrsUnits, OffTerm, OffYear, Offering.FacSSN, FacFirstName, FacLastName, OffTime, OffDays FROM Faculty, Course, Offering WHERE FacDept = 'MS' AND Faculty.FacSSN = Offering.FacSSN AND Offering.CourseNo = Course.CourseNo

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Column Renaming

Example 2: create a view containing offering data and the number of enrolled students.

CREATE VIEW Enrollment_View ( OfferNo, CourseNo, Term, Year, Instructor, NumStudents ) AS SELECT Offering.OfferNo, CourseNo, OffTerm, OffYear, FacLastName, COUNT(*) FROM Offering, Faculty, Enrollment WHERE Offering.FacSSN = Faculty.FacSSN AND Offering.OfferNo = Enrollment.OfferNo GROUP BY Offering.OfferNo, CourseNo, OffTerm, OffYear, FacFirstName, FacLastName

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Using Views

Example 3 SELECT OfferNo, CourseNo, FacFirstName, FacLastName, OffTime, OffDays FROM MS_View WHERE OffTerm = 'SPRING' AND OffYear = 2003

Example 4 SELECT OfferNo, Instructor, NumStudents, CrsUnits FROM Enrollment_View, Course WHERE Enrollment_View.CourseNo = Course.CourseNo AND NumStudents < 5

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Processing View Queries Materialization

Execute two queries Large overhead Preferred in static environments such as data

warehouses (Chapter 16)

Modification Substitute view definition for view references Execute one query Incurs little overhead Not possible for all view queries

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View Modification

Modify SQL EngineQueryV QueryB

Results

QueryV: query that references a view

QueryB: modification of QueryV such that references to the view are replaced by references to base tables.

DB

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View Materialization

View

SQL Engine ResultQuery d

Query v: Query that referencesa view

Query v

Query d: Query that defines aview

DB

SQL Engine

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Modification Examples

Example 5: Query using a view

SELECT OfferNo, CourseNo, FacLastName FROM MS_View WHERE OffYear = 2006

Example 6: Modified query

SELECT OfferNo, Course.CourseNo, FacLastName FROM Faculty, Course, Offering WHERE FacDept = 'MS' AND OffYear = 2006 AND Faculty.FacSSN = Offering.FacSSN AND Offering.CourseNo = Course.CourseNo

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Single Table Updatable Views Support modification statements Rules for single table updatable views

1-1 correspondence between view rows and base table rows

View includes PK of base table View includes all required columns View definition does not have GROUP BY or

DISTINCT

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Updatable View Examples

Example 7: Single table updatable view CREATE VIEW Fac_View1 AS SELECT FacSSN, FacFirstName, FacLastName, FacRank, FacSalary, FacDept, FacCity, FacState, FacZipCode FROM Faculty WHERE FacDept = 'MS'

Example 8: View update UPDATE Fac_View1 SET FacSalary = FacSalary * 1.1 WHERE FacRank = 'ASST'

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View Update with Side Effects

• Modify column used in the WHERE condition of a view definition

• Use WITH CHECK OPTION clause to prevent

Example 9: Change the department of rows in the Fac_View1 UPDATE Fac_View1 SET FacDept = 'FIN' WHERE FacSalary > 100000

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Multiple Table Updatable Views No industry standard Only recently supported More complex rules than single table

updatable views Access supports flexible view updates for

multi-table views Oracle rules in Appendix 10.B

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1-M Updatable Queries Associated with 1-M relationships Join column of the parent table: primary key or

unique Determine updatable tables Child table updatable

Primary key Foreign key: must include in the query result Required columns of the child table

Include primary key and required columns to support insert operations on the parent table

Use join operator style

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1-M Updatable Query Example

Example 10: Save as Course_Offering_View1 SELECT Course.CourseNo, CrsDesc, CrsUnits, Offering.OfferNo, OffTerm, OffYear, Offering.CourseNo, OffLocation, OffTime, FacSSN, OffDays FROM Course INNER JOIN Offering ON Course.CourseNo = Offering.CourseNo

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Usage of a 1-M Updatable Query

Example 11: Insert a row into the Course_Offering_View1.

INSERT INTO Course_Offering_View1 ( OfferNo, Offering.CourseNo, OffTerm, OffYear, OffLocation, OffTime, FacSSN, OffDays ) VALUES ( 7799, 'IS480', 'Spring', 2003, 'BLM201', '1:30PM', '098-76-5432', 'MW' )

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Extensions to Multiple Tables

Apply rules to each 1-M relationship FK of each child table in the query result Usually only the lowest level child table is

updatable Examples

Course-Offering, Faculty-Offering Offering-Enrollment, Faculty-Offering

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Hierarchical Forms

Formatted window for data entry and display

Main form Subform Provide attractive interface for a 1-M

relationship Specification of data requirements is

important

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Revised University Database

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Example Hierarchical Form

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Analysis of Data Requirements

Identify the 1-M relationship Identify the linking fields Determine other tables in the main form

and the subform Determine updatable tables Write queries for the main form and

subform

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Registration Form Requirements

1-M relationship: Registration-Enrollment Linking fields: Registration.RegNo,

Enrollment.RegNo Other tables

Main form: Student Subform: Offering, Course, Faculty

Updatable tables: Registration, Enrollment

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Registration Main Form QuerySELECT RegNo, RegTerm, RegYear, RegDate, Registration.StdSSN, Registration.StdSSN, RegStatus, StdFirstName, StdLastName, StdClass, StdCity, StdState FROM Registration INNER JOIN Student ON Registration.StdSSN = Student.StdSSN

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Registration Subform QuerySELECT RegNo, Enrollment.OfferNo, OffTime, Offering.CourseNo, OffLocation, OffTerm, OffYear, Offering.FacSSN,

FacFirstName, FacLastName, CrsDesc, CrsUnits FROM ( ( Enrollment INNER JOIN Offering ON Enrollment.OfferNo = Offering.OfferNo ) INNER JOIN Course ON Offering.CourseNo = Course.CourseNo ) LEFT JOIN Faculty ON Faculty.FacSSN = Offering.FacSSN

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Faculty Assignment Form

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Faculty Assignment Requirements

Step 1: Faculty (parent table), Offering (child table)

Step 2: Faculty.FacSSN, Offering.FacSSN Step 3: Course table in the subform Step 4: update Offering.FacSSN

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Faculty Assignment Queries Main form

SELECT FacSSN, FacFirstName, FacLastName, FacDept FROM Faculty

SubformSELECT OfferNo, Offering.CourseNo, FacSSN, OffTime, OffDays, OffLocation, CrsUnits FROM Offering INNER JOIN COURSE ON Offering.CourseNo = Course.CourseNo

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Hierarchical Reports Stylized presentation of data appropriate

to a selected audience Use nesting (or indentation) to provide a

visually appealing layout Vocabulary

Group: sorted field; usually indented Detail line: innermost field

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Example Hierarchical Report

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Summary Data in Detail Lines

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Query Formulation Skills Less difficult than skills for forms Inspect report

Match fields in the report to database columns Determine the needed tables Identify the join conditions

Determine the level of detail Row data versus summary data Query should provide data for the detail lines

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Faculty Work Load QuerySELECT Offering.OfferNo, FacFirstName, FacLastName, FacDept, OffTerm, CrsUnits, OffLimit, Count(Enrollment.RegNo) AS NumStds, NumStds/Offlimit AS PercentFull, (NumStds/Offlimit) < 0.25 AS LowEnrollment FROM Faculty, Offering, Course, Enrollment WHERE Faculty.FacSSN = Offering.FacSSN AND Course.CourseNo = Offering.CourseNo AND Offering.OfferNo = Enrollment.OfferNo AND ( ( Offering.OffTerm = 'Fall' AND Offering.OffYear = 2005 ) OR ( Offering.OffTerm = 'Winter' AND Offering.OffYear = 2006 ) OR ( Offering.OffTerm = 'Spring' AND Offering.OffYear = 2006 ) ) GROUP BY Offering.OfferNo, FacFirstName, FacLastName, FacDept, OffTerm, CrsUnits, OffLimit

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Summary Significant benefits with a modest

performance penalty Foundation of application data

requirements Updatable views important for hierarchical

forms Carefully analyze data requirements

before developing forms and reports