IT420: Database Management and
Organization
SQL Views, Triggers and Stored Procedures
17 February 2006
Adina Crăiniceanu
www.cs.usna.edu/~adina
1
Last time
 SQL Views
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Today
 Updates on views
 Triggers
 Stored procedures
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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
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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
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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
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Using Views
 Customer(CustID,
CustName, Address,
Phone)
 CREATE VIEW CustomerV AS
SELECT *
FROM Customers
Customers
CustID
CustName
01
Amy Gale
Annapolis, MD 410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
05
Address
Phone
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
SELECT * FROM CustomerV query result:
 SELECT *
FROM CustomerV
CustID
CustName
01
Amy Gale
Annapolis, MD 410-293-5234
02
Tom Smith
Baltimore, MD
05
Kroenke, Database Processing
Address
Phone
443-56747899
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
7
Using Views
 CREATE VIEW CustomerV AS
SELECT *
FROM Customers
 SELECT *
FROM CustomerV
WHERE Address LIKE
‘%Annapolis%’
Customers
CustID
CustName
01
Amy Gale
Annapolis, MD 410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
05
Address
Phone
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
SELECT query result:
CustID
CustName
01
Amy Gale
05
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Address
Phone
Annapolis, MD 410-293-5234
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
8
UPDATE on Views
 CREATE VIEW CustomerV AS
SELECT *
FROM Customers
 UPDATE CustomerV
SET Phone = ‘410-123-1234’
WHERE CustID = 01
UPDATE impacts the
Customers table
Customers table before update:
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
05
Customers table after update:
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-123-1234
02
Tom Smith
Baltimore, MD
443-56747899
05
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
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INSERT on Views
 CREATE VIEW CustomerV AS
SELECT *
FROM Customers
 INSERT INTO CustomerV
VALUES(‘08’,’Scott
White’,’DC’,’401-456-3415’)
INSERT impacts the
Customers table
Customers table
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
05
Customers table after insert:
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-123-1234
02
Tom Smith
Baltimore, MD
443-56747899
05
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
08
Scott White
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DC
401-456-3415
10
DELETE on Views
 CREATE VIEW CustomerV AS
SELECT *
FROM Customers
 DELETE FROM CustomerV
WHERE Address LIKE
‘%Annapolis%’
Customers table
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
05
Customers table after delete:
CustID
CustName
Address
Phone
02
Tom Smith
Baltimore, MD
443-56747899
DELETE impacts the
Customers table
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Using Views – Case 2
 Customer(CustID, CustName,
Address, Phone)
 CREATE VIEW CustomerV2
AS
SELECT CustID, CustName,
Phone
FROM Customers
 SELECT *
FROM CustomerV2
Customers
CustID
CustName
01
Amy Gale
Annapolis, MD 410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
05
Address
Phone
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
SELECT * FROM CustomerV2 query result:
CustID
CustName
Phone
01
Amy Gale
410-293-5234
02
Tom Smith
443-5674-7899
05
Chris O’Neal
410-295-6583
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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’)
Address NOT NULL, INSERT
fails
Customers table
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-293-5234
02
Tom Smith
Baltimore, MD 443-5674-7899
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
05
Customers table after insert:
CustID
CustName
Address
Phone
01
Amy Gale
Annapolis
410-123-1234
02
Tom Smith
Baltimore, MD
443-56747899
05
Chris O’Neal Annapolis, MD 410-295-6583
- 21402
08
Scott White
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NULL
401-456-3415
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Views – Case 3
 Rental(RentalID, CustID,
PlaneID, NbHours, HRate)
 CREATE VIEW RentalView AS
SELECT RentalID, CustID,
PlaneID, NbHours*HRate
AS Charge
FROM Rental
 SELECT *
FROM RentalView
Rental
RentalID
CustID
PlaneID
NbHours
HRate
01
111
01
3
$400
02
111
13
7
$250
05
112
01
1
$420
SELECT * FROM RentalView query result:
RentalID
CustID
PlaneID
Charge
01
111
01
$1200
02
111
13
$1750
05
112
01
$420
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INSERT on Views – Case 3
 CREATE VIEW RentalView AS
SELECT RentalID, CustID,
PlaneID, NbHours*HRate
AS Charge
FROM Rental
 INSERT INTO RentalView
VALUES (03,113,01,1250)
INSERT fails!
UPDATE Charge fails!
Rental
RentalID
CustID
PlaneID
NbHours
HRate
01
111
01
3
$400
02
111
13
7
$250
05
112
01
1
$420
SELECT * FROM RentalView query result:
RentalID
CustID
PlaneID
Charge
01
111
01
$1200
02
111
13
$1750
05
112
01
$420
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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
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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
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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
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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
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Create trigger
 CREATE TRIGGER trigger_name
ON table_or_view_name
AFTER | BEFORE | INSTEAD OF
INSERT | UPDATE | DELETE
AS
trigger_code
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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
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Create trigger
Declare variables
Built-in function
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Trigger for Referential Integrity
Actions – generic code
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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
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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
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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
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Triggers vs. Stored Procedures
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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
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