matthew p. johnson, ocl2, cisdd cuny, january 20051 ocl2 oracle 10g: sql & pl/sql session #1...

Matthew P. Johnson, OCL2, CISDD CUNY, January 2005

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OCL2 Oracle 10g:SQL & PL/SQLSession #1

Matthew P. Johnson

CISDD, CUNY

January, 2005


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Personnel Instructor: Matthew P. Johnson

mattpj-at-gmail.com

TA: Ratna Priya Moganti rmoganti7-at-yahoo.com

Admin: Dawn Kleinberger dkleinberger-at-gc.cuny.edu


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Communications Web page:

http://pages.stern.nyu.edu/~mjohnson/oracle/

syllabus

course policies

reading assignments

etc.


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Acknowledgements Thanks to Ramesh at NYU, Ullman, et al.,

Raghu and Johannes, Dan Suciu, Arthur Keller, David Kuijt for course materials

See classpage for other related, antecedent DBMS courses


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What is a Database? A very large, integrated collection of data. Models real-world enterprise.

Entities students, courses, instructors, TAs

Relationships George is currently taking OCL2 Dick is currently teaching OCL2 Condi is currently TA-ing OCL2 but took it last semester

Database Management System (DBMS): large software package designed to store and manage databases


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Databases are everywhere: Ordering a pizza Databases involved?1. Pizza Hut’s DB

stores previous orders by customer stores previous credit cards used

2. Credit card records huge databases of (attempted) purchases location, date, amount, parties

3. Got approved by credit-report companies4. phone company’s records

Local Usage Details (“Pull his LUDs, Lenny.”)

5. Caller ID ensures reported address matches destination


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Your wallet is full of DB records Driver’s license Credit cards Medical insurance card Social security card Gym membership Individual checks Dollar bills (w/serial numbers) Maybe even photos (ids on back)


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Databases are everywhere Q: Websites backed by DBMSs?

retail: Amazon, etc. data-mining: “Page You Made”

search engines: Google, etc. directories: Internic, etc. searchable DBs: IMDB, tvguide.com, etc.

Q: Non-web examples of DBMSs? airline bookings criminal/terrorist: TIA NYPD’s CompStat

all serious crime stats by precinct Retailers: Wal-Mart, etc.

when to re-order, purchase patterns, data-mining Genomics!


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Example of a Traditional DB App Suppose we are building a system to store

the information about: checking accounts savings accounts account holders state of each of each person’s accounts


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Can we do it without a DBMS?Sure we can! Start by storing the data in files:

checking.txt savings.txt customers.txt

Now write C or Java programs to implement specific tasks


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Doing it without a DBMS... Transfer $100 from George’s savings acc to

checking:

Read ‘savings.txt’Find & update the record “George”

balance -= 100

Write ‘savings.txt’Read ‘checking.txt’Find & update the record “George”

balance += 100

Write ‘checking.txt’

Read ‘savings.txt’Find & update the record “George”

balance -= 100

Write ‘savings.txt’Read ‘checking.txt’Find & update the record “George”

balance += 100

Write ‘checking.txt’

Write a C program to do the following:


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Problems without a DBMS...1. System crashes:

Q: What is the problem? A: George lost his $100 Same problem even if reordered

2. Simultaneous access by many users George and Dick visit ATMs at same Lock checking.txt before each use– what is the problem?

Read ‘savings.txt’Find&update the rec “George.”Write ‘savings.txt’Read ‘checking.txt’Find&update the rec “George”Write ‘checking.txt’

Read ‘savings.txt’Find&update the rec “George.”Write ‘savings.txt’Read ‘checking.txt’Find&update the rec “George”Write ‘checking.txt’ CRASH !


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Problems without an DBMS...

3.Large data sets (say 50GB) Why is this a problem?

No indices Finding “George” in huge flatfile is expensive

Modifications intractable without better data structures “George” “Georgie” is very expensive Deletions are very expensive


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Problems without a DBMS...

5.Security? File system may be insecure File system security may be coarse

6.Application programming interface (API)? suppose need other apps to access DB

7.How to interact with other DBMSs?


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General problems to solve In building our own system, many Qs arise:

how do we store the data? (file organization, etc.) how do we query the data? (write programs…) make sure that updates don’t mess things up?

leave the DB “consistent” provide different views on the data?

e.g., ATM user’s view v. bank teller’s view how do we deal with crashes?

Too hard! Go buy Oracle! Q: How does a DBMS solve these problems? A: Long story; see other courses/books


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Big issue: Transaction processing Grouping of several queries (or other

database actions) into one transaction ACID properties

Atomicity all or nothing

Consistency constraints on relationships

Isolation concurrency control Simulated solipsism

Durability Crash recovery


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Atomicity & Durability Saw how George lost $100 with makeshift DBMS Real DBMSs prevent this outcome

xacts are all or nothing

One idea: Keep a log (history) of all actions in set of xacts Durability: Use log to redo or undo certain ops in

crash recovery Atomicity: don’t really commit changes until end

Then, all at once


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Isolation Concurrent execution is essential for performance.

Frequent, slow disk accesses don’t waste CPU – keep running

Interleaving actions of different user programs can lead to inconsistency:

e.g., two programs simultaneously withdraw from the same account

DBMS ensures such problems don’t arise: users can pretend they are using a single-user system


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Isolation Contrast with a file in two Notepads

Strategy: ignore multiple users whichever saves last wins first save is overwritten

Contrast with a file in two Words Strategy: blunt isolation One can edit To the other it’s read-only


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Consistency Each xant (on a consistent DB) must leave it

in a consistent state can define integrity constraints checks the defined claims about the data remain

true


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Data Models Every DBMS uses some data model:

collection of concepts for describing data Schema: description of partic set of data,

using some data model Relational data model: most widely used (by

far) data model Oracle, DB2, SQLServer, other SQL DBMSs main concept: relation ~ table of rows & columns a rel’s schema defines its fields


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Example: university database Conceptual schema:

Students(ssn: string, name: string, login: string, age: int, gpa: real)

Courses(cid: string, cname: string, credits: int) Enrolled(sid:string, cid:string, grade: string)

Physical schema: Relations stored as unordered text files. Indices on first column of each rel

External Schema (View): Course_info(ssn: string, name: string) My_courses(cname: string, grade: string)


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How the programmer sees the DBMS Start with DDL to create tables:

Continue with DML to populate tables:

CREATE TABLE Students (Name CHAR(30)SSN CHAR(9) PRIMARY KEY NOT NULL,Category CHAR(20)

) . . .

CREATE TABLE Students (Name CHAR(30)SSN CHAR(9) PRIMARY KEY NOT NULL,Category CHAR(20)

) . . .

INSERT INTO StudentsVALUES(‘Howard, ‘123456789’, ‘undergraduate’). . . .

INSERT INTO StudentsVALUES(‘Howard, ‘123456789’, ‘undergraduate’). . . .


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How the programmer sees the DBMS Tables:

Still implemented as files, but behind the scenes can be quite complex

SSN Name Category 123-45-6789 Howard undergrad 234-56-7890 Wesley grad … …

Students:

CID CName C20.0046 Databases C20.0056 Advanced Software

Courses:

“data independence” = separate logical view from physical implementation

SSN CID semester 123-45-6789 C20.0046 Spring,

2004 123-45-6789 C20.0056 Spring,

2004 234-56-7890 C20.0046 Fall, 2003 …

Takes:


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Querying: Structured Query Language Find all the students who have taken OCL2:

SELECT SSNFROM TakesWHERE CID=“OCL2”

Find all the students who OCL2 last fall: SELECT SSN

FROM TakesWHERE CID=“OCL2” AND Semester=“Fall, 2003”

Find the students’ names: SELECT Name

FROM Students, TakesWHERE Students.SSN=Takes.SSN AND CID=“OCL2” AND Semester=“Fall, 2003”

Query processor does this efficiently


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Database Industry Relational databases are a great success of

theoretical ideas based on most “theoretical” type of math there is: set theory

DBMS companies are among the largest software companies in the world

Oracle, IBM (with DB2), Microsoft (SQL Server, Microsoft Access), Sybase

Also opensource: MySQL, PostgreSQL, etc. $20B+ industry XML (“semi-structured data”) also important

New lingua franca for exchanging data


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The Study of DBMS Several aspects:

Modeling and design of databases DBMS programming: querying and update DBMS implementation

This course covers all three though more time on first two

Also will look at some more advanced areas XML, data-mining, LDAP?


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Databases are used by DB app programmers

desktop app programmers web developers

Database administrators (DBAs) design schemas security/authorization crash recovery tuning

Everyone else (perhaps indirectly) “You may not be interested in databases, but

databases are interested in you.” - Trotsky


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Course outline Two biggest topics:

SQL PL/SQL

But also:

Database design: Entity/Relationship models Modeling constraints

The relational model: Relational algebra Transforming E/R models to relational schemas


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Outline (Continued) SQL views and triggers Connecting to a Oracle from programming

languages Web apps XML

May change as course progresses partly in response to audience


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Textbook Oracle Database 10g PL/SQL 101

by Christopher Allen Hardcover: 416 pages Publisher: McGraw-Hill/

Osborne Media ISBN: 0072255404 1 edition (August 10, 2004) Distributed in class


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SQL Readings Optional reference: SQL in a Nutshell

Online (free) SQL tutorials include:

SQL for Web Nerds (http://philip.greenspun.com/sql/)

A Gentle Introduction to SQL (http://sqlzoo.net/)


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On-going Feedback Don’t wait until the class is over to give

feedback on improving it too late for you then!

Send mail if you have questions or concerns

“We’re in touch, so you be in touch.”


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Summary DBMS used to maintain, query large datasets

Benefits include recovery from system crashes, concurrent access, data integrity, security, and quick application development

Database skills are critical in financial services, marketing and other business areas!


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So what is this course about, really?A bit of everything! Languages: SQL, XPath, XQuery Data modeling Some theory!

Functional dependencies, normal forms e.g., how to find most efficient schema for data

Lots of implementation and hacking in end-of-course project

Business DBMS examples/cases Most importantly: how to meet real-world needs


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For right now: written survey Email to mattpj-at-gmail.com: name email previous cs/is/math/logic courses/background previous programming experience

Perl? PHP? HTML?

Job: programmer, DBA, etc. why taking class


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Agenda Last time: intro, RDBMS, ACID test This time: E/R model1. Identify entity sets, relations and attributes2. One-one, one-many, many-many relations3. Simple ER diagrams to model a situation4. 3-way relationships; Converting to binary5. Entities with multiple roles6. Subclasses Design issues1. Principles of faithfulness & simplicity in ER diagrams2. Redundancy3. Whether an element should be an attribute or entity set4. Replacing a relationships with entity sets


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DB development path

the

WorldE/R

design

Relational

schema

Relational

DB


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Entity Relationship (E/R) Model A popular data model – useful to database

designers Graphical representation of miniworld Helps design the database, not implement it E/R design is translated to a relational design

relational design then implemented in an RDBMS Elements of model

Entities Entity Sets Attributes Relationships (!= relations!)


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Elements of E/R Model: Entity Sets Entity: like an object

e.g. President Bush Particular instance of a concept

Entity set: set of one sort of entities or a concept e.g. World leaders Generally, same set of attributes

Represented by a rectangle A “good” entity set – you decide

Common properties Correspond to class of phys. or bus. objects

(People, products, accounts, grades, etc.)

World Leader


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Elements of E/R Model: Attributes Properties of entities in entity set

Like fields in a struct Like columns in a table/spreadsheet Like data members in an object

Values in some domain (e.g., ints, strings) Represented by ovals: Assumed atomic

But could have limited structure Ints, strings, etc.

ID Name

Student


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Elements of E/R Model: Relationships Connect two or more entity sets

e.g. students enroll in courses Binary relationships: connect two entity sets –

most common Multiway relationships: connect several entity

sets Represented by diamonds

Students Enroll Courses


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Elms of E/R Model: Rel’ships (cont’d) Students Enroll in courses Courses are Held in rooms The E/R data model:

Students Enroll Courses

Held

Rooms

NameID


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A little set theory A mathematical set a collection of members A set is defined by its members

“Are you in or are you out?” No other structure, no order, no duplicates allowed

Sets specified by listing: {1, 2, 3, …} = N {1, 2, George Bush} (not useful in DBMS)

Or by “set-builder” notation: { x in N: 2 divides x} = ? { x in Presidents | reelected(x)} = ? {2x: x in N} = ?


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A little set theory One set can be a subset of another (which is then a

superset of it) ReelectedPresidents is a subset of Presidents Also, RP is a proper subset of Pres – some lost reelection

Given two sets X and Y, the cross product or Cartesian product isX x Y = {(x,y): x in X, y in Y}= the set of all ordered pairs in which the first comes from X and the second comes from Y

Important: (x,y) != {x,y} In an order pair or tuple

Order matters Duplicates are allowed


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A little set theory Mathematically, a relation(ship) between X and Y is

just a subset of X x Y= all those pairs (x,y) s.t. x is related to y

Example: owner-of O on People, Cats O(MPJ, Gödel) holds

The equals relation E on N, N: E(3,3) holds because 3 = 3 E(3,4) does not hold E is still a set: E = {(1,1), (2,2), (3,3), …}

Father of relation F on People, People: F(GHWB, GWB) holds F(GWB, GHWB) does not hold Relations aren’t necessarily symmetric


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Many-many

Multiplicity of Relationships

Many-one One-one

Representation of relationships No arrow: many-to-many Sharp arrow: many-to-one Rounded arrow: “exactly one”

“key constraint” One-one:


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Multiplicity of Relationships

Students Enrolls Courses

Many-to-many:

Student Live Residence hall

Many to one: a student lives in <= 1 residence hall

Many to exactly one: a student must live in a residence hall

Student Live Residence hall


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Multiplicity, set-theoretically Assume: no vars below are equal Many-one means:

if (x1,y1) in R then (x1,y2) cannot be in R One-many means:

if (x1, y1) in R then (x2,y1) cannot be in R One-one means:

if (x1,y1) in R, then neither (x1,y2) nor (x2,y1) can be in R

Notice: one-one is stronger than many-one One-one implies both many-one and one-

many


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E/R Diagram

Students CoursesEnrolls

ID

Name

ID

Name

Assisting

TAID

Name


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E/R Diagrams Works if each TA is a TA of all students.

Connection student-TA is only through the course

But what if students were divided into sections, each section with a separate TA? Then, a student in OCL2 would be related to only

one of the TAs for OCL2. Which one?

3-way relationship is helpful here


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Multiway Relationships

Students

Courses

TAs

Enrolls

Students Courses TAsAlberto OCL2 DonaldRichard OCL2 PaulBernard OCL2 Colin… … …

Enrolls entries:

NB: Enrolls determines TA:

(student, course) at most one TA


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Converting multiway relships to binary Some models limit relationships to binary Multiway relationship – equivalent collection of binary,

many to one relationships Replace relationship with connecting entity set

Students

Courses

TAs

EnrollsStudent-of

Course-of

TA- ofNB: Enrolls has no attributes!


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Second multiway e.g.: renting movies Scenario: a Customer Rents a Movie from a

VideoStore on a certain date

Q: Which entity does date belong to? A: To the fact of the renting Relationships can have attributes

always (implicitly) many-one

Rental

VideoStore

Customer

Movie

date


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Second multiway e.g.: renting movies But they don’t have to Relationship attributes can be replaced with

(trivial) new entities

Rental

VideoStore

Customer

Movie

date

Date


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Where can we draw arrows?

(store, video, customer) date ? Date is a relship att, implicitly determined

(store, video, date) customer ? (store, date, customer) video ? (video, date, customer) store ?

Second multiway e.g.: renting movies

Rental

VideoStore

Customer

Movie

date


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Arrow-drawing Q: Why does it matter? Round arrow benefit:

Obvious: One item takes less space than many Less obvious: easier to access one item x than set of

one item {x} In programming: an int v. a linked list with just one int

Regular arrow benefit: Mapping to a set of either one elm or none seems bad But not implemented this way Always one element, but that value may be NULL

Lesson: it pays to identify your relship’s multiplicity


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Second multiway e.g.: renting movies

Convert to binary?Rental

VideoStore

Customer

Movie

date

Rental

Customer

Store

Movie

StoreOf

MovieOf

BuyerOf

date


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Roles in relationships Entity set appears more than once in a relship

Generally distinct entities Each appearance is in a different role Edges labeled by roles

Pre-req

Prereq

Successor

Course

Course (Pre-req)

Course (Successor)

Accounting Finance-I

Finance-I Derivatives

Finance-I Finance-II

Calculus Derivatives


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Subclasses in the E/R model Some entities are special cases of other Conversely: some are generalizations

Humans are specialized mammals Grad students are specialized students

And, in turn, specialized mammals NB: These aren’t examples but subclasses

Subclass A isa B Represented by a triangle Always one-to-one, though arrows omitted Root is more general Multiple inheritance is allowed! A single entity may consist of all components (sets of

fields) in arbitrary ESs and their ancestors


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Subclasses

Movies

Cartoons Murder-Mysteries

isa isaVoices

Weapon

stars

length title year

Lion King

Component

“Lion King”: atts of Movies; relship Voices

“Roger Rabbit”: atts of Movies; relship Voices; att weapon

Roger Rabbit

TX Chainsaw Massacre


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E/R inheritance v. OO inheritance In a OOP class hierarchy, children also inherit

“attributes” from parents But an object is an instance of one class

In E/R, an entity may be composed of components from multiple, not-directly-related ESs Roger Rabbit is composed of components from Cartoons,

Murder Mysteries, and Movies We could create a Cartoon Murder Mysteries ES if there

were any atts specific to them

So the real difference: In E/R, can have implicit multiple inheritance between any set of IS-A-connected nodes (sharing a root)


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Design Principles Faithfulness Avoiding redundancy Simplicity Choice of relationships Picking elements


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Faithfulness Is the relationship many-many or many-one? Are the attributes appropriate? Are the relationships applicable to the

entities? Examples

Courses & instructors maybe many-one, maybe many-many

Bosses & subordinates maybe one-many, maybe many-many


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Simplicity Einstein: Theories as simple as possible, but not

simpler. Use as few elements as possible

Minimum required relations No unnecessary attributes (will you be using this

attribute?) Eliminate “spinning wheels”

Example: how can we simplify this?

Movies Ownings StudiosOwned-by Owns


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Avoiding redundancy Say everything exactly once

Minimize database storage requirements More important: prevent possible update errors

simplest but not only e.g.: modify data one place but not the other – more later

Example: Spot the redundancy

Studios MoviesOwn

StudioName

Name

Length

Name

Address


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Next time We’ll finish E/R models and begin the

relational model Readings will be posted

matthew p. johnson, ocl2, cisdd cuny, january 20051 ocl2 oracle 10g: sql & pl/sql session #1...

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