1 Designing Tables for an Oracle Database System Database Course, Fall 2004.

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Designing Tables for an Designing Tables for an Oracle Database SystemOracle Database System

Database Course, Fall 2004

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From theory to practiceFrom theory to practice

• The Entity-Relationship model: a convenient way of representing the world.

• The Relational model: a model of organizing data using tables.

• Oracle: a database infrastructure which implements the relational model.

• Converting ER->Relational model is important!

• SQL(Structured Query Language): A language used to get information from an oracle database.

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TechnicalitiesTechnicalities

• Add the following to your .cshrc file:

source ~db/oraenv

• You will be able to use Oracle after you log

out and log in again.

• You can run Oracle from os, pita, inferno,

etc. Cannot run from xil-es.

• If you are on xil, do rlogin to one of these

computers (e.g., rlogin inferno-01)

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Connecting to the Oracle Connecting to the Oracle DatabaseDatabase

At the command line prompt, write:

sqlplus login/[email protected]

In the beginning your password is the same as your login. You can change your password with the command:

password

To disconnect, type: quit

Remember: (almost) Every command must end with a semicolon (;)

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Running Commands from Running Commands from an .sql Filean .sql File

• Instead of typing commands into the SQLPLUS terminal, you can load commands from a file (no special format is required).

• Invoke by:1. Use the command @file from SQLPLUS to load the file

file.sql

Or:

2. Invoke the SQLPLUS command with the extra parameter @file to load the file at connection:

sqlplus login/[email protected] @file

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Spooling the OutputSpooling the Output

• Output can be placed in a file:

– spool myFile.out

(output file updates after next command)

• Spooling can be turned off with:

– spool off

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TablesTables

• The basic element in oracle is a table.

• A table has columns (attributes), and rows

(tuples).

• Every column has a Name and Type (of the

data it stores), and some columns have

constraints.

• Some tables may have additional

constraints.

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Creating Tables in SQLCreating Tables in SQL

Id Name Dept. Age

0345 Eyal Sales 28

0965 Yair Transport 34

7665 Ori Warehous

e

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Creating a TableCreating a Table

The basic format of the CREATE TABLE

command is:

CREATE TABLE TableName(

Column1 DataType1 ColConstraint, …

ColumnN DataTypeN ColConstraint,

TableConstraint1, …

TableConstraintM

);

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An ExampleAn Example

CREATE TABLE Employee(ID NUMBER NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1),Salary NUMBER(5) NOT NULL,Dept NUMBER

);

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An Example (cont.)An Example (cont.)

Oracle is case insensitive in Column names!

If you type describe Employee you get:Name Null? Type

----------- ------------ ------------

SSN NOT NULL NUMBER

FNAME VARCHAR2(20)

LNAME VARCHAR2(20)

GENDER CHAR(1)

SALARY NOT NULL NUMBER(5)

DEPT NUMBER

Notice that “describe” describes the structure and not the contents of the table.

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Examples of Data TypesExamples of Data Types

CHAR(n) String of length n (n <= 2000)

VARCHAR2(n) Variable length string of size <= n (n <=

4000)

LONG Variable length string of length (<= 2GB)

CLOB Character large object (<= 4GB)

BLOB Binary large object (<= 4GB)

DATE Valid dates (up to seconds)

TIMESTAMP Valid timestamps (up to milliseconds)

NUMBER Up to 40 digits

NUMBER(n) Integer of size n

NUMBER(n,m) Number of size n with m digits after

decimal place

Others XML, Abstract types, etc.

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• What happens if we insert:– 'abc' into char(5)?

– 'abc' into varchar(5)?

– 'abc' into char(2)?

– 'abc' into varchar(2)?

– 105.32 into number(3,2)?

– 105.32 into number(5,2)?

– 105.32 into number(4,1)?

– 105.32 into number(3)?

– 105.32 into number?

– 105.1 into number(7,5) ?

• Why not always use number and not number(n,m)?

• Why not always use varchar2(4000) or long?

• Where is the boolean datatype?

“abc““abc “

105.32

Wrong!

105.32

105.3105

Wrong!

Wrong!

Wrong!

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Constraints in Create TableConstraints in Create Table

• Adding constraints to a table enables the database system to enforce data integrity.

• However, adding constraints also makes inserting data slower.

• Different types of constraints:

* Not Null * Default Values

* Unique * Primary Key

* Foreign Key * Check Condition

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Not Null ConstraintNot Null Constraint

CREATE TABLE Employee(SSN NUMBER NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1),Salary NUMBER(5) NOT NULL,Dept NUMBER

);

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Default Values Default Values

CREATE TABLE Employee(SSN NUMBER NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER

);

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Unique Constraint (Syntax Unique Constraint (Syntax 1)1)

CREATE TABLE Employee(SSN NUMBER UNIQUE NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER

);

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Unique Constraint (Syntax Unique Constraint (Syntax 2)2)

CREATE TABLE Employee(SSN NUMBER NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER,UNIQUE(SSN)

);

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Unique Constraint Unique Constraint (Another Example)(Another Example)

CREATE TABLE Employee(SSN NUMBER UNIQUE NOT NULL,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER,UNIQUE(Fname, Lname)

);

How else can this be written?

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Primary Key ConstraintPrimary Key Constraint

CREATE TABLE Employee(SSN NUMBER PRIMARY KEY,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER,UNIQUE(Fname, Lname)

);

Primary Key implies: * NOT NULL * UNIQUE. There can only be one primary key.

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Primary Key Constraint Primary Key Constraint (Syntax 2)(Syntax 2)

CREATE TABLE Employee(SSN NUMBER,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER,UNIQUE(Fname, Lname),PRIMARY KEY(ssn)

);

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Another TableAnother Table

CREATE TABLE Department(Dept NUMBER PRIMARY KEY,Name VARCHAR2(20),ManagerId NUMBER

);

Shouldn’t all department numbers in Employee appear in Department?

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Foreign Key ConstraintForeign Key ConstraintCREATE TABLE Employee(

ID NUMBER PRIMARY KEY,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER, UNIQUE(Fname, Lname),FOREIGN KEY (Dept) REFERENCES

Department(Dept));

NOTE: Dept must be unique (or primary key) in Department

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Foreign Key Constraint Foreign Key Constraint (Syntax 2)(Syntax 2)

CREATE TABLE Employee(ID NUMBER PRIMARY KEY,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’),Salary NUMBER(5) NOT NULL,Dept NUMBER, UNIQUE(Fname, Lname),FOREIGN KEY (Dept) REFERENCES

Department);

NOTE: Dept must be the name of the field in Department, too

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Foreign KeyForeign Key

ID FName LName Gende

r

Sallary Dept

02334 Larry Bird M 230000 12

04556 Magic Johnson M 270000 45

Foreign Key

Dept Name ManID

12 Sales 988

45 Repair 876

Employee

Department

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Understanding Foreign Understanding Foreign KeysKeys

• The constraint on the last table should be read as:

“The field Dept in Employee is a foreign key that

references the field Dept in Department”

• Meaning: Every non-null value in the field Dept of

Employee must appear in the field Dept of

Department.

What happens to Employees in department 312 when Department 312 is removed from the Department table?

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Deleting a Referenced Deleting a Referenced ValueValue

• If nothing additional is specified, then Oracle will not allow Department 312 to be deleted if there are Employees working in this department.

• If the constraint is written as

FOREIGN KEY (Dept) REFERENCES Department ON DELETE CASCADE

then Employees working in 312 will be deleted automatically from the Employee table, when 312 is deleted from Departments

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Cyclic Foreign KeysCyclic Foreign Keys

CREATE TABLE Department(Dept NUMBER PRIMARY KEY,Name VARCHAR2(20),ManagerId NUMBER, FOREIGN KEY (ManagerId) REFERENCES Employee(SSN)

);

Do you see a problem in defining these tables and in inserting data now?

We should revise the Department table:

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Foreign KeyForeign Key

ID FName LName Gender Sallary Dept

Foreign Key

Dept Name ManID

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Solution to Cyclic Solution to Cyclic ConstraintsConstraints

Add one of the constraints later on (after insertion):

CREATE TABLE Department(Dept NUMBER PRIMARY KEY,Name VARCHAR2(20),ManagerId NUMBER);

Insert data here…

ALTER TABLE Department

ADD(FOREIGN KEY (ManagerId)

REFERENCES Employee(SSN));

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Check ConditionsCheck Conditions

• A check condition is a Boolean expression:

– “And”s and “Or”s of conditions of the type X >

5…

• On a column: it can refer only to the column

• On a table: it can refer only to multiple

columns in the table

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Check ConstraintsCheck Constraints

CREATE TABLE Employee(SSN NUMBER PRIMARY KEY,Fname VARCHAR2(20),Lname VARCHAR2(20),Gender CHAR(1) DEFAULT(‘F’)

CHECK(Gender = ‘F’ or Gender = ‘M’) ,Salary NUMBER(5) NOT NULL,CHECK (Gender = ‘M’ or Salary > 10000)

);

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Deleting a TableDeleting a Table

• To delete the table Employee :

DROP TABLE Employee;

• Mind the order of dropping when there are

foreign key constraints. Why?

• Can use:

DROP TABLE Employee cascade constraints;

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Translating ER-Diagrams to Translating ER-Diagrams to Table DefinitionsTable Definitions

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Relations vs. TablesRelations vs. Tables

• We show how to translate ER-Diagrams to table definitions

• Sometimes, people translate ER-Diagrams to relation definition, which is more abstract than table definitions.– e.g., Employee(SSN, Fname, Lname, Gender,

Salary, Dept);

– table definitions contain, in addition, constraints and datatypes

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Simple entity translationSimple entity translation

General Rule:

• Create a table with the name of the Entity.

• There is a column for each attribute

• The key in the diagram is the primary key of the table

Actorid

name address

birthday

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Simple entity translationSimple entity translation

create table Actor(id varchar2(20) primary key,

name varchar2(40),

birthday date,

address varchar2(100));

Actorid

name address

birthday

Relation: Actor (id, name, birthday, address)

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Translating Entities with Translating Entities with Relationships Relationships (without constraints)(without constraints)

• Create tables for the entities as before

• Create a table with the name of the relationship

• Relationship table attributes: its own attributes (salary) + all keys of the relating entities (title, id).

Q: What is the primary key of the table?

A: A composite of both entity keys

Q: What foreign keys are needed?

A: From the relationship table to the entities

Actorid

name

address

birthday

Acted In Film

title

type

year

salary

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Translating relationships Translating relationships (without constraints)(without constraints)

What would be the relation for ActedIn?

How would you define the table for ActedIn?

Actorid

name

address

birthday

Acted In Film

title

type

year

salary

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Translating Recursive Translating Recursive Relationships Relationships

(without constraints)(without constraints)

Employeeid

name

address

Manages

manager

worker

Relation: Manages (Wid, Mid)

What would be the table definition?create table Manages( Eid varchar2(20), Mid varchar2(20), Foreign key Eid references Employee(id), Foreign key Mid references Employee(id), Primary key(Eid, Mid));

If we want to make sure an employee is not his own manager we

can express it with Check

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Translating relationshipsTranslating relationships(key constraints): Option 1(key constraints): Option 1

Option 1:

• Same as without key constraints (3 tables), except that the relationship primary key is…?

title.

Directorid

name

Directed Film title

salary year

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create table Directed(

id varchar2(20),

title varchar2(40),

salary integer,

primary key (title),

foreign key id references Director,

foreign key title references Film);

Directorid

name

Directed Film title

salary year

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Option 2:• Do not create a table for the relationship

• Add information columns that would have been in the relationship's table to the table of the entity with the key constraint

• Why couldn’t we do this with a regular relation?

Directorid

name

Directed Film title

salary year

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create table Film(

title varchar2(40),

year integer,

primary key (title),

id varchar2(20),

salary integer,

foreign key(id) references Director);

Directorid

name

Directed Film title

salary year

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Translating relationshipsTranslating relationships(key constraints)(key constraints)

• What are the different options for

translating this diagram?

A R B

C

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Translating relationshipsTranslating relationships(participation constraints)(participation constraints)

General Rule:

• If both participation and key constraint exist, use

Option 2 from before (only 2 tables).

• Add the not null constraint to ensure that there will

always be values for the key of the other entity

Directorid

name

Directed Film title

salary year

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create table Film(

title varchar2(40),

year integer,

id varchar2(20),

salary integer,

foreign key (id) references Director,

primary key (title));

Directorid

name

Directed Film title

salary year

Where should we add NOT NULL?

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• How would we translate this?

Actorid

name

Acted In Film title

salary year

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Translating Weak Entity Translating Weak Entity SetsSets

create table award(

name varchar2(40),

year integer,

money number(6,2),

o_name varchar2(40),

primary key(name, year, o_name),

foreign key (o_name) references Organization(name)

on delete cascade

)

Award

Organization

Gives

year

name

name

phonenumber

money

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Translating ISA:Translating ISA:Option 1Option 1

create table MoviePerson( ... )

create table Actor(id varchar2(20),

picture bfile,

primary key(id),

foreign key (id) references MoviePerson))

create table Director(...)

Movie Person

ISA

id

name

address

picture DirectorActor

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Translating ISA:Translating ISA:Option 2Option 2

No table for MoviePerson!

create table Actor(id varchar2(20),

address varchar2(100),

name varchar2(20),

picture blob,

primary key(id));

create table Director(...)

Movie Person

ISA

id

name

address

picture DirectorActor

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Which Option To Choose?Which Option To Choose?

• What would you choose if:

– Actor and Director DO NOT COVER

MoviePerson?

– Actor OVERLAPS Director?

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Translating Translating AggregationAggregation

• Create table for Won using:– key of ActedIn

– key of Award (careful, award is a weak entity)

Actorpicture

Filmyear

typetitle

Acted Insalary

Award

Organization

Gives

year

name

name

phonenumber

Won

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SummarySummary

Tables Primary key Remarks

Simple Entity Single table The entity key a column for

each attr.

Simple

Relationship

3 (2 entities

+relationship)

For the

relation: Both

entity keys

Foreign keys

from rel. Table

Key constraint 3 as before or

2 (one for each

entity)

Key of

constrained

ent.

Foreign keys

from rel. Table

Foreign key from

constr. Entity

Key and

Participation

constr.

2 Regular Constrained

entity has a

non-null f. key

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Tables Primary key Remarks

Weak Entity 2: parent and

weak entities

Weak: its own

and parent

keys

Foreign keys

from weak ent.

ISA: covers

and no

overlap

2: only child

entities

Parent key

ISA: otherwise 3: parent and

child entities

Parent key Foreign keys

from child ent.

Aggregation 3: 2

aggregates

and

relationship

For

relationship:

keys of both

aggregates

Foreign keys

from

relationship

table

1 Designing Tables for an Oracle Database System Database Course, Fall 2004.

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