Download Creating a Table

Designing Tables for an Oracle
Database System
Database Course, Fall 2005
1
From 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.
2
Technicalities
• Add the following to your .cshrc file:
if (-r ~db/oraenv) source ~db/oraenv
• You will be able to use Oracle after you
log out and log in again.
• You can run Oracle from computers pita,
inferno, etc.
3
Sqlplus
• Oracle is a commercial, hardware-based,
heavy(!), program.
• To connect to it, we use the Sqlplus utility.
• The Sqlplus program accepts commands in
standard SQL and sends them to the Oracle
database.
• The interface creates a “local” database for
each user.
4
Connecting to the Oracle Database
• At the command line prompt, write:
Sqlplus
(not sqlplus !)
• This will give you access to the “personal” database of
‘user’ (In other words, to access “your” database, you
have to run it from your own CS account).
• You will be presented with a Sqlplus console, in which you
type your commands.
• To disconnect (and return to your regular shell), type:
quit
• Remember: (almost) Every command must end with a
semicolon (;)
5
6
Reminder
The database is kept on the disk, so
anything you create will be there next time
you log on.
sailors
Reserves
Main
Memory
DISK
CPU
7
Running Commands from an .sql File
•
Instead of typing commands into the SQLPLUS
terminal, you can load commands from a file (no special
format is required).
•
The file name should end with “.sql”
•
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 @file
8
Spooling the Output
• Output can be placed in a file:
spool <file_name>
• Spooling can be turned off with:
spool off
9
Tables
• 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.
10
Creating Tables in SQL
Id
Name
Dept.
Age
0345
Eyal
Sales
28
0965
Yair
Transport
34
7665
Ori
Warehouse 31
11
Creating 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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Example
CREATE TABLE Employee(
ID
NUMBER NOT NULL,
Fname VARCHAR2(20),
Lname VARCHAR2(20),
Gender CHAR(1),
Salary NUMBER(5) NOT NULL,
Dept
NUMBER
);
13
An Example (cont.)
Oracle is case insensitive in Column names!
If you type describe Employee you get:
Name
Null?
Type
----------- ------------ -----------ID
NOT NULL NUMBER
FNAME
VARCHAR2(20)
LNAME
VARCHAR2(20)
GENDER
CHAR(1)
SALARY
DEPT
NOT NULL NUMBER(5)
NUMBER
Notice that “describe” describes the
structure and not the contents of the table.
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Examples of Data Types
CHAR(n)
String of fixed length n (n <= 2000)
VARCHAR2(n)
Variable length string of size <= n (n <= 4000)
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 varchar(5)?
“abc “
“abc“
– 'abc' into char(2)?
Wrong!
– 'abc' into varchar(2)?
Wrong!
– 105.32 into number(3,2)?
Wrong!
– 105.32 into number(5,2)?
105.32
105.3
105
– 'abc' into char(5)?
– 105.32 into number(4,1)?
– 105.32 into number(3)?
– 105.32 into number?
– 105.1 into number(7,5) ?
105.32
Wrong!
• Why not always use number and not number(n,m)?
• Why not always use varchar2(4000)?
• Where is the boolean datatype?
16
Constraints 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 Constraint
CREATE TABLE
SSN
Fname
Lname
Gender
Salary
Dept
);
Employee(
NUMBER NOT NULL,
VARCHAR2(20),
VARCHAR2(20),
CHAR(1),
NUMBER(5) NOT NULL,
NUMBER
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Default Values
CREATE TABLE
SSN
Fname
Lname
Gender
Salary
Dept
);
Employee(
NUMBER NOT NULL,
VARCHAR2(20),
VARCHAR2(20),
CHAR(1) DEFAULT(‘F’),
NUMBER(5) NOT NULL,
NUMBER
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Unique Constraint (Syntax 1)
CREATE TABLE
SSN
Fname
Lname
Gender
Salary
Dept
);
Employee(
NUMBER UNIQUE NOT NULL,
VARCHAR2(20),
VARCHAR2(20),
CHAR(1) DEFAULT(‘F’),
NUMBER(5) NOT NULL,
NUMBER
20
Unique Constraint (Syntax 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)
);
21
Unique Constraint
(Another Example)
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(Fname, Lname)
);
Can this be written differently?
22
Primary 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
(Syntax 2)
CREATE TABLE Employee(
SSN
NUMBER,
Fname
VARCHAR2(20),
Lname
VARCHAR2(20),
Gender
CHAR(1) DEFAULT(‘F’),
Salary
NUMBER(5) NOT NULL,
DeptNumber NUMBER,
UNIQUE(Fname, Lname),
PRIMARY KEY(ssn)
);
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Another Table
CREATE TABLE Department(
DeptNumber NUMBER PRIMARY KEY,
Name
VARCHAR2(20),
ManagerId NUMBER
);
Shouldn’t all department numbers in
Employee appear in Department?
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Foreign Key Constraint
CREATE TABLE Employee(
ID
NUMBER PRIMARY KEY,
Fname
VARCHAR2(20),
Lname
VARCHAR2(20),
Gender
CHAR(1) DEFAULT(‘F’),
Salary
NUMBER(5) NOT NULL,
DeptNumber
NUMBER,
UNIQUE(Fname, Lname),
FOREIGN KEY (DeptNumber)
REFERENCES Department(DeptNumber)
);
DeptNumber must be unique (or primary key) in Department
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Foreign Key Constraint (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,
DeptNumber
NUMBER,
UNIQUE(Fname, Lname),
FOREIGN KEY (DeptNumber)
REFERENCES Department
);
NOTE: You can use this syntax only if the name of the
fields in both tables are identical
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Employee
Foreign Key
ID
FName
LName
Gender
Sallary
Dept
02334
Larry
Bird
M
230000
12
04556
Magic
Johnson M
270000
45
Foreign Key
Department
Dept
Name
ManID
12
Sales
988
45
Repair
876
28
Understanding Foreign Keys
• 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?
29
Deleting a Referenced Value
• If nothing additional is specified, then Oracle will not
allow Department 312 to be deleted if there are
Employees working in (referencing to) 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
30
Foreign Keys
We should revise the Department table:
CREATE TABLE Department(
DeptNumber 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?
31
Foreign Key
ID
FName
LName
Gender
Sallary
DeptNum
Foreign Key
DeptNum Name
ManID
32
Solution to Cyclic Constraints
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));
33
Check 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
34
Check 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)
);
35
Deleting 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;
36
Converting ER-Diagrams to Table
Definitions
37
General Principals
•
When converting ER diagrams to
Relations, we should try to:
1. Reduce duplicate information
2. Constrain as tightly as possible
•
Note:
1. Some scenarios can be represented in different
ways.
2. Sometimes we will not be able to fully represent
constraints, or will be forced to represent
information more than once.
38
Relations 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
39
Simple entity translation
id
name
birthday
Actor
address
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
40
Simple entity translation
id
birthday
Actor
name
address
Relation: Actor (id, name, birthday, address)
create table Actor(id varchar2(20) primary key,
name varchar2(40),
birthday date,
address varchar2(100));
41
Translating Entities with
Relationships
birthday
id
Actor
(without constraints)
Acted In
title
Film
year
name
address
salary
type
• 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
42
Translating relationships
(without constraints)
birthday
id
Actor
Acted In
Film
title
year
name
address
salary
type
How would you define the table for ActedIn?
43
Translating Recursive Relationships
(without constraints)
manager
id
Employee
name
worker
Manages
address
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
44
Translating relationships
(key constraints): Option 1
id
Director
Directed
name
salary
Film
title
year
Option 1:
• Same as without key constraints (3 tables), except that
the relationship primary key is…?
title.
45
Translating relationships
(key constraints): Option 1
id
Director
Directed
name
Film
salary
title
year
create table Directed(
id varchar2(20),
title varchar2(40),
salary integer,
primary key (title),
foreign key id references Director,
foreign key title references Film);
46
Translating relationships
(key constraints): Option 2
id
Director
name
Directed
Film
salary
title
year
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
47
Translating relationships
(key constraints): Option 2
id
Director
Directed
name
Film
title
year
salary
create table Film(
title varchar2(40),
year integer,
primary key (title),
Why couldn’t we do
this when there
were no
constraints?
id varchar2(20),
salary integer,
foreign key(id) references Director);
48
Translating relationships
(participation constraints)
id
Director
name
Directed
salary
Film
title
year
General Rule:
• If both participation and key constraint exist, use
Option 2 from before (only 2 tables), and:
• Add the not null constraint on the referncing attribute
to ensure that there will always be values for the key of
the other entity
49
Translating relationships
(participation constraints)
id
Director
Directed
name
Film
title
year
salary
create table Film(
title varchar2(40),
year integer,
id varchar2(20),
Where should we add
NOT NULL?
salary integer,
foreign key (id) references Director,
primary key (title));
50
Translating relationships
(participation constraints)
id
name
Actor
Acted In
salary
Film
title
year
• How would we translate this?
51
Translating Weak Entity Sets
phone
number
name
create table award(
name varchar2(40),
year integer,
Organization
money number(6,2),
o_name varchar2(40),
Gives
primary key(name, year, o_name),
Award
year
foreign key (o_name) references
Organization(name)
money
on delete cascade
name
)
52
Translating ISA:
Option 1
address
id
Movie Person
name
ISA
picture
Actor
Director
create table MoviePerson( ... )
create table Actor(id varchar2(20),
picture bfile,
primary key(id),
foreign key (id) references MoviePerson))
create table Director(...)
53
Translating ISA:
Option 2
address
id
Movie Person
name
ISA
picture
Actor
Director
No table for MoviePerson!
create table Actor(id varchar2(20),
address varchar2(100),
name varchar2(20),
picture blob,
primary key(id));
create table Director(...)
54
Which Option To Choose?
• What would you choose if:
– Actor and Director DO NOT COVER
MoviePerson?
– Actor OVERLAPS Director?
55
Oname
Translating
Aggregation
phone
number
Organization
picture
salary
Gives
Director
ID
Acted In
Won
Award
year
Broadcasted
name
year
Film
title
type
Won(title, year, name, Oname, Broadcasted);
56
Summary
Simple Entity
Tables
Primary key
Remarks
Single table
The entity key
a column for
each attr.
Simple
3 (2 entities
For the relation: Foreign keys
Relationship
+relationship)
Both entity keys from rel. Table
Key constraint
3 as before or
Key of
Foreign keys
constrained ent. from rel. Table
Foreign key from
2 (one for each
constr. Entity
entity)
Key and
2
Regular
Constrained
Participation
entity has a
constr.
non-null f. key
57
Tables
Primary key
Remarks
2: parent and
Weak: its own
Foreign keys
weak entities
and parent keys from weak ent.
ISA: covers
2: only child
Parent key
and no overlap
entities
ISA: otherwise
3: parent and
Weak Entity
Parent key
child entities
Aggregation
Foreign keys
from child ent.
3: 2 aggregates
For
Foreign keys
and relationship
relationship:
from relationship
keys of both
table
aggregates
58