1 IT420: Database Management and Organization SQL Views, Triggers and Stored Procedures 17 February...

1

IT420: Database Management and Organization

SQL Views, Triggers and Stored Procedures17 February 2006

Adina Crăiniceanuwww.cs.usna.edu/~adina

http://www.cs.usna.edu/~adina

Kroenke, Database Processing 2

Last time

SQL Views


Today

Updates on views Triggers Stored procedures


SQL Views

SQL view is a virtual table that is constructed from other tables or views

It has no data of its own, but obtains data from tables or other views

It only has a definition


CREATE VIEW Command

CREATE VIEW command:CREATE VIEW view_name AS select_statement

Use the view: In SELECT statements Sometimes in INSERT statements Sometimes in UPDATE statements Sometimes in DELETE statements


Uses for SQL Views

Security: hide columns and rows Display results of computations Hide complicated SQL syntax Provide a level of isolation between actual data

and the user’s view of data three-tier architecture

Assign different processing permissions to different views on same table

Assign different triggers to different views on same table


Using Views

Customer(CustID, CustName, Address, Phone)

CREATE VIEW CustomerV AS

SELECT *

FROM Customers

SELECT *

FROM CustomerV

CustID CustName Address Phone

01 Amy Gale Annapolis, MD 410-293-5234

02 Tom Smith Baltimore, MD 443-5674-7899

05 Chris O’Neal Annapolis, MD - 21402

410-295-6583





410-295-6583

Customers

SELECT * FROM CustomerV query result:


Using Views


SELECT *

FROM Customers

SELECT *

FROM CustomerV

WHERE Address LIKE ‘%Annapolis%’





410-295-6583




410-295-6583

Customers

SELECT query result:


UPDATE on Views


SELECT *

FROM Customers

UPDATE CustomerV

SET Phone = ‘410-123-1234’

WHERE CustID = 01


01 Amy Gale Annapolis 410-293-5234



410-295-6583





410-295-6583

Customers table before update:

Customers table after update:

UPDATE impacts the Customers table


INSERT on Views


SELECT *

FROM Customers

INSERT INTO CustomerV

VALUES(‘08’,’Scott White’,’DC’,’401-456-3415’)





410-295-6583





410-295-6583

08 Scott White DC 401-456-3415

Customers table

Customers table after insert:

INSERT impacts the Customers table


DELETE on Views


SELECT *

FROM Customers

DELETE FROM CustomerV

WHERE Address LIKE ‘%Annapolis%’





410-295-6583



Customers table

Customers table after delete:

DELETE impacts the Customers table


Using Views – Case 2

Customer(CustID, CustName, Address, Phone)

CREATE VIEW CustomerV2 AS

SELECT CustID, CustName, Phone

FROM Customers

SELECT *

FROM CustomerV2





410-295-6583

CustID CustName Phone

01 Amy Gale 410-293-5234

02 Tom Smith 443-5674-7899

05 Chris O’Neal 410-295-6583

Customers

SELECT * FROM CustomerV2 query result:


INSERT on Views - Case 2

CREATE VIEW CustomerV2 AS

SELECT CustID, CustName, Phone

FROM Customers

INSERT INTO CustomerV2

VALUES(‘08’,’Scott White’,’401-456-3415’)





410-295-6583





410-295-6583

08 Scott White NULL 401-456-3415

Customers table

Customers table after insert:

Address NOT NULL, INSERT fails


Views – Case 3 Rental(RentalID, CustID,

PlaneID, NbHours, HRate)

CREATE VIEW RentalView ASSELECT RentalID, CustID,

PlaneID, NbHours*HRate AS Charge

FROM Rental

SELECT * FROM RentalView

RentalID CustID PlaneID NbHours HRate

01 111 01 3 $400

02 111 13 7 $250

05 112 01 1 $420

RentalID CustID PlaneID Charge

01 111 01 $1200

02 111 13 $1750

05 112 01 $420

Rental

SELECT * FROM RentalView query result:


INSERT on Views – Case 3 CREATE VIEW RentalView

ASSELECT RentalID, CustID,

PlaneID, NbHours*HRate AS Charge

FROM Rental

INSERT INTO RentalViewVALUES (03,113,01,1250)

INSERT fails!

UPDATE Charge fails!

RentalID CustID PlaneID NbHours HRate

01 111 01 3 $400

02 111 13 7 $250

05 112 01 1 $420

RentalID CustID PlaneID Charge

01 111 01 $1200

02 111 13 $1750

05 112 01 $420

Rental

SELECT * FROM RentalView query result:


Updateable Views

Views based on a single table No computed columns All non-null columns present in view

Views with INSTEAD OF triggers defined on them

Views based on a single table, primary key in view, some non-null columns missing from view Updates for non-computed columns ok Deletes ok Inserts not ok


Triggers

Trigger: stored program that is executed by the DBMS whenever a specified event occurs

Associated with a table or view Three trigger types: BEFORE, INSTEAD

OF, and AFTER Each type can be declared for INSERT,

UPDATE, and DELETE Resulting in a total of nine trigger types


Programming Languages for Triggers Depends on DBMS

Java or PL/SQL for Oracle T-SQL for SQL Server

C++, C#, Visual Basic .NET for SQL Server 2005


Firing Triggers

When a trigger is fired, the DBMS supplies: Old and new values for the update New values for inserts Old values for deletions

The way the values are supplied depends on the DBMS product

Trigger applications: Provide default values Enforce data constraints Update views Perform referential integrity actions


Create trigger

CREATE TRIGGER trigger_name

ON table_or_view_name

AFTER | BEFORE | INSTEAD OF

INSERT | UPDATE | DELETE

AS

trigger_code


Trigger for Complex Default Value

Trans(TransactionID, WorkID, AcquisitionPrice, AskingPrice)

ArtistWorkNet(SaleID, WorkID, NetPrice)

AskingPrice = max of 2*AcquisitionPrice AcquisitionPrice+AVG(Past_NetPrice), if

WorkID already in table


Declare variables

Create trigger

Built-in function


Trigger for Referential Integrity Actions – generic code


Class Exercise

Students(Alpha, LName, FName, GPA) Enroll(Alpha, CourseID, Semester, Grade) GradeValues(LetterGrade, PointValue)

Define a trigger to update the GPA every time the student gets a new grade, or a grade changes


Stored Procedures

A stored procedure is a program that is stored within the database and is compiled when used In Oracle, it can be written in PL/SQL or Java In SQL Server, it can be written in TRANSACT-SQL

Stored procedures can receive input parameters and they can return results

Stored procedures can be called from: Programs written in standard languages, e.g., Java, C# Scripting languages, e.g., JavaScript, VBScript SQL command prompt, e.g., SQL*Plus, Query Analyzer


Stored Procedure Advantages

Greater security as store procedures are always stored on the database server

SQL can be optimized by the DBMS compiler Code sharing resulting in:

Less work Standardized processing Specialization among developers


Triggers vs. Stored Procedures


Project 1 – Due March 3, 2006

National College Learning Center Organization (NCLCA) www.nclca.org Membership Conferences organized

Have: Partial user requirements (forms) Tasks:

Design the ER model Transform ER model to tables Verify tables are normalized Write SQL to create the tables in SQL Server Write SQL to answer typical user queries Write-up explaining your work

1 IT420: Database Management and Organization SQL Views, Triggers and Stored Procedures 17 February...

Documents

Transcript of 1 IT420: Database Management and Organization SQL Views, Triggers and Stored Procedures 17 February...