1. Logical DB Design: ER to Relational
Entity sets to tables.
Employees
ssn
name
lot
The slides for this text are organized into several modules. Each lecture contains about enough material for a 1.25 hour class period. (The time estimate is very approximate--it will vary with the instructor, and lectures also differ in length; so use this as a rough guideline.) This covers Lectures 1 and 2 (of 6) in Module (5).
Module (1): Introduction (DBMS, Relational Model)
Module (2): Storage and File Organizations (Disks, Buffering, Indexes)
Module (3): Database Concepts (Relational Queries, DDL/ICs, Views and Security)
Module (4): Relational Implementation (Query Evaluation, Optimization)
Module (5): Database Design (ER Model, Normalization, Physical Design, Tuning)
Module (6): Transaction Processing (Concurrency Control, Recovery)
Module (7): Advanced Topics
CREATE TABLE Employees
(ssn CHAR(11),
name CHAR(20),
lot INTEGER,
PRIMARY KEY (ssn)) 3

2. Constraints in Create Table
Adding constraints to a table enables the database system to enforce data integrity.
Different types of constraints:
* Not Null * Default Values
* Unique * Primary Key
* Foreign Key * Check Condition

3. Null and Not Null
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Relational Data Model

4. Primary Key Constraint
CREATE TABLE Student (
ID NUMBER PRIMARY KEY,
Fname VARCHAR2(20) NOT NULL,
Lname VARCHAR2(20) NOT NULL, );
Primary Key implies: * NOT NULL * UNIQUE.
There can only be one primary key.

5. Primary Key Constraint (Syntax 2)
CREATE TABLE Students (
ID NUMBER,
Fname VARCHAR2(20) NOT NULL,
Lname VARCHAR2(20) NOT NULL,
PRIMARY KEY(ID) );
Needed when the primary key is made up of two or more fields

6. Relationship Sets to Tables
ssn
name
lot
did
dname
budget
Employees
Departments
Works_in
since
CREATE TABLE Works_In (
ssn CHAR(11),
did INTEGER,
since DATE,
PRIMARY KEY (ssn, did),
FOREIGN KEY (ssn)
REFERENCES Employees,
FOREIGN KEY (did)
REFERENCES Departments)
We implement a Many-to-Many relationship by adding 2 Tables’ Primary Keys to a third Table
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Relational Data Model

7. Foreign Key Constraint
CREATE TABLE Studies(
Course NUMBER,
Student NUMBER,
FOREIGN KEY (Student) REFERENCES
Students(ID) );
NOTE: ID must be unique (or primary key) in Student

8. Foreign Keys in SQL
Only students listed in the Students relation should be allowed to enroll for courses
CREATE TABLE Enrolled (
sid CHAR(20), cid CHAR(20), grade CHAR(2),
PRIMARY KEY (sid, cid),
FOREIGN KEY (sid) REFERENCES Students )
Enrolled
sid
cid
grade
53666
Carnatic101 C
Reggae203 B
53650
Topology112 A
History105
Students
sid
name
login
age
gpa
53666
Jones 18
3.4
53688
Smith
3.2
53650 19
3.8
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Relational Data Model

9. Key Constraints Translation to relational model?
since
lot
name
ssn
dname
Each dept has at most one manager, according to the key constraint on Manages.
did
budget
Manages
Employees
Departments
Translation to
relational model?
1-to-1
1-to Many
Many-to-1
Many-to-Many 6

10. ER Relationship Sets  Relations
since
ssn
name
lot
did
dname
budget
Manages
Employees
Departments
CREATE TABLE
Employees (
ssn CHAR(11),
name CHAR(20),
lot INTEGER,
PRIMARY KEY (ssn))
CREATE TABLE Manages (
ssn CHAR(11),
did INTEGER,
since DATE,
PRIMARY KEY (ssn, did),
FOREIGN KEY (ssn)
REFERENCES Employees,
FOREIGN KEY (did)
REFERENCES Departments)
CREATE TABLE
Departments (
did INTEGER,
dname CHAR(20),
budget REAL,
PRIMARY KEY (did))
With the key constraint?
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Relational Data Model

11. … with Key Constraints Map relationship Manages to one table:
Note that did is the key
Separate tables for Employees and Departments
CREATE TABLE
Departments (
did INTEGER,
dname CHAR(20),
budget REAL,
PRIMARY KEY (did))
CREATE TABLE Manages (
ssn CHAR(11),
did INTEGER,
since DATE,
PRIMARY KEY (did),
FOREIGN KEY (ssn)
REFERENCES Employees,
FOREIGN KEY (did)
REFERENCES Departments)
Relational Data Model
CS174A

12. Improvements Using Key Constraints
CREATE TABLE
Departments (
did INTEGER,
dname CHAR(20),
budget REAL,
PRIMARY KEY (did))
CREATE TABLE Manages (
ssn CHAR(11),
did INTEGER,
since DATE,
PRIMARY KEY (did),
FOREIGN KEY (ssn)
REFERENCES Employees,
FOREIGN KEY (did)
REFERENCES Departments)
CREATE TABLE Dept_Mgr (
did INTEGER,
dname CHAR(20),
budget REAL,
ssn CHAR(11),
since DATE,
PRIMARY KEY (did),
FOREIGN KEY (ssn)
REFERENCES Employees)
Since each department has a unique manager, we could instead combine Manages and Departments
Relational Data Model
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13. Review: Participation Constraints
Does every department have a manager?
If so, this is a participation constraint: the participation of Departments in Manages is said to be total (vs. partial)
Every did value in Departments must appear in a row of Manages (with a non-null ssn value!)
since
ssn
name
lot
did
dname
budget
Manages
Employees
Departments
Works_In
since
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Relational Data Model

14. Participation Constraints in SQL
We can capture participation constraints involving one entity set in a binary relationship, but little else (without resorting to CHECK constraints)
CREATE TABLE Dept_Mgr (
did INTEGER,
dname CHAR(20),
budget REAL,
ssn CHAR(11) NOT NULL,
since DATE,
PRIMARY KEY (did),
FOREIGN KEY (ssn) REFERENCES Employees
ON DELETE NO ACTION)
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Relational Data Model

15. Review: Weak Entities
A weak entity can be identified uniquely only by considering the primary key of another (owner) entity
Owner entity set and weak entity set must participate in a one-to-many relationship set (1 owner, many weak entities)
Weak entity set must have total participation in this identifying relationship set
under pname denotes a partial key.
both relationship set and entity set are thick lines.
cost
ssn
name
lot
pname
age
Policy
Employees
Dependents
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Relational Data Model

16. Translating Weak Entity Sets
Weak entity set and identifying relationship set are translated into a single table
When the owner entity is deleted, all owned weak entities must also be deleted
CREATE TABLE Dep_Policy (
pname CHAR(20),
age INTEGER,
cost REAL,
ssn CHAR(11) NOT NULL,
PRIMARY KEY (pname, ssn),
FOREIGN KEY (ssn) REFERENCES Employees
ON DELETE CASCADE)
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Relational Data Model

17. Translating ISA: Option 1
address
Translating ISA: Option 1 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(...)

18. Translating ISA: Option 2
address
Translating ISA: Option 2 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(...)

19. Review: ISA Hierarchies
Overlap constraints:
Can Joe be an Hourly_Emps as well as a Contract_Emps entity? (Allowed/disallowed)
Covering constraints:
Does every Employees entity also have to be an Hourly_Emps or a Contract_Emps entity? (Yes/no)
Reasons for using ISA:
To add descriptive attributes specific to a subclass
To identify entities that participate in a relationship
ssn
name
lot
Employees
ISA
Hourly_Emps
Contract_Emps
Hourly_wages
contractid
Hours_worked
Relational Data Model
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20. Translating ISA Hierarchies to Relations
General approach: 3 relations Employees, Hourly_Emps and Contract_Emps
Every employee is recorded in Employees
For hourly employees, extra info recorded in Hourly_Emps (hourly_wages, hours_worked, ssn) must delete Hourly_Emps tuple if referenced Employees tuple is deleted
Queries involving all employees easy, those involving just Hourly_Emps require a join to get some attributes
Alternative: Just Hourly_Emps and Contract_Emps
Hourly_Emps : ssn, name, lot, hourly_wages, hours_worked
Each employee must be in one of these two subclasses
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Relational Data Model

21. Views
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Relational Data Model

22. What is a View?
In SQL, a VIEW is a virtual relation based on the result-set of a SELECT statement.
A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database. In some cases, we can modify a view and present the data as if the data were coming from a single table.
Syntax:
CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition

23. SQL – Relations, Tables & Views
When we say Relation, it could be a Table or a View. There are three kind of relations:
Stored relations tables
We sometimes use the term “base relation” or “base table”
Virtual relations views
Temporary results

24. SQL – Create View
Example: Create a view with title and year and made by Paramount studio.
Movie (title, year, length, inColor, studioName, producerC#)
CREATE VIEW ParamountMovie AS
SELECT title,year
FROM Movie
WHERE studioName = ‘Paramount’;

25. The SQL Query Language
The most widely used relational query language. Current standard is SQL-99
To find all 18 year old students, we can write:
SELECT *
FROM Students S
WHERE S.age=18
sid
name
login
age
gpa
53666
Jones 18
3.4
53688
Smith
3.2
To find just names and logins, replace the first line:
SELECT S.name, S.login
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Relational Data Model

26. SQL - Basic Queries
Example: Pose a query to get the names of all students: SELECT LastName, FirstName FROM Students

27. SQL - Basic Queries (cont.)
Names of freshmen students

28. SQL - Basic Queries –Joining tables based on foreign key
Connecting majors with their department chairs: we need to have ChairID = FacultyID
Majors(MajorID, MajorName, Department, ChairID)
Faculty (FacultyID, FirstName, LastName, Phone, )

29. SQL - Basic Queries – Joining tables
Student last name, advisor last name
OR (aliasing)

30. SQL - Basic Queries – Joining tables

31. ** END **