Chapter 10 Application Development with Views

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Outline Background Creating views and using views Processing queries that reference views Updatable views Data requirements for hierarchical forms Data requirements for reports

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. What is a View? Derived table Behaves like a base table (virtual) Stored query

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. View Advantages Reduce impact of database definition changes Simplify database usage Unit of database security Can be a performance penalty on complex views

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Three Schema Architecture

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Processing View Queries Materialization –Execute two queries –Large overhead –Preferred in static environments Modification –Substitute view definition for view references –Execute one query –Incurs little overhead –Not possible for all view queries

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Modification Example Example 5: Query using a view SELECT OfferNo, CourseNo, FacLastName FROM MS_View WHERE OffYear = 2003 Example 6: Modified query SELECT OfferNo, Course.CourseNo, FacLastName FROM Faculty, Course, Offering WHERE FacDept = 'MS' AND OffYear = 2003 AND Faculty.FacSSN = Offering.FacSSN AND Offering.CourseNo = Course.CourseNo

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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'

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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 >

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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#, ' ', 'MW' )

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Revised University Database

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Example Hierarchical Form

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Data Requirements for the Registration Form 1-M relationship: Registration-Enrollment Linking fields: Registration.RegNo, Enrollment.RegNo Other tables –Main form: Student –Subform: Offering, Course, Faculty Updatable tables: Registration, Enrollment

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Registration Main Form Query SELECT RegNo, RegTerm, RegYear, RegDate, Registration.StdSSN, Registration.StdSSN, RegStatus, StdFirstName, StdLastName, StdClass, StdCity, StdState FROM Registration INNER JOIN Student ON Registration.StdSSN = Student.StdSSN

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Registration Subform Query SELECT 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Faculty Assignment Form

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Data Requirements for the Faculty Assignment Form 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Faculty Assignment Queries Main form SELECT FacSSN, FacFirstName, FacLastName, FacDept FROM Faculty Subform SELECT OfferNo, Offering.CourseNo, FacSSN, OffTime, OffDays, OffLocation, CrsUnits FROM Offering INNER JOIN COURSE ON Offering.CourseNo = Course.CourseNo

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Example Hierarchical Report

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Summary Data in Detail Lines

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Query Formulation Skills for Reports 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

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. Faculty Work Load Query SELECT 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 = 2002 ) OR ( Offering.OffTerm = 'Winter' AND Offering.OffYear = 2003 ) OR ( Offering.OffTerm = 'Spring' AND Offering.OffYear = 2003 ) ) GROUP BY Offering.OfferNo, FacFirstName, FacLastName, FacDept, OffTerm, CrsUnits, OffLimit

McGraw-Hill/Irwin © 2004 The McGraw-Hill Companies, Inc. All rights reserved. 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