Database Basics

CPSC 4670/5670

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Purpose of a Database

• The purpose of a database is to keep track of things

• Unlike a list or spreadsheet, a database may store information that is more complicated than a simple list

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Database Systems• The four components of a database system

are:• Users• Database Application• Database Management System (DBMS)• Database

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Users, Database

• A user of a database system will• Use a database

application to track things

• Use forms to enter, read, delete and query data

• Produce reports

• A database is a self-describing collection of related records

• Self-describing• The database itself

contains the definition of its structure

• Metadata is data describing the structure of the database data

• Tables within a relational database are related to each other

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Database Management System (DBMS)

• A database management system (DBMS) serves as an intermediary between database applications and the database

• The DBMS manages and controls database activities

• The DBMS creates, processes and administers the databases it controls

• Create databases• Create tables• Create supporting

structures• Read database data• Modify database data

(insert, update, delete)• Maintain database

structures• Enforce rules i.e.,

Referential Integrity Constraints

• Control concurrency• Provide security• Perform backup and

recovery

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Database Applications• A database application is a set of one or

more computer programs that serves as an intermediary between the user and the DBMS

• A database application• Create and process forms• Process user queries• Create and process reports• Execute application logic• Control database applications

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Desktop Database Systems• Desktop database systems typically:

• Have one application• Have only a few tables• Are simple in design• Involve only one computer• Support one user at a time

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Organizational Database Systems

• Organizational database systems typically:• Support several users

simultaneously• Include more than one

application• Involve multiple

computers• Are complex in design• Have many tables• Have many databases

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Commercial DBMS Products

• Example Desktop DBMS Products• Microsoft Access

• Example Organizational DBMS Products• Oracle’s Oracle• Microsoft’s SQL Server• IBM’s DB2• InterSystems Caché®

http://www.intersystems.com/cache/

The Relational Model

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Relational Databases• Relational databases are designed to

address many of the information complexity issues

• A relational database stores information in tables. Each informational topic is stored in its own table.

• In essence, a relational database will break-up a list into several parts. One part for each theme in the list.

• A Project List would be divided into a CUSTOMER Table, a PROJECT Table, and a PROJECT_MANAGER Table

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Entity

• An entity is something of importance to a user that needs to be represented in a database

• An entity represents one theme or topic

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Relation

• A relation is a two-dimensional table that has specific characteristics

• The table dimensions, like a matrix, consist of rows and columns

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Characteristics of a Relation

• Rows contain data about an entity• Columns contain data about attributes

of the entity• Cells of the table hold a single value• All entries in a column are of the same

kind• Each column has a unique name• The order of the columns is unimportant• The order of the rows is unimportant• No two rows may be identical

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A Sample Relation

EmployeeNumber

FirstName

LastName

100 Mary Abermany

101 Jerry Caldera

104 Alea Copley

107 Murugan Jacksoni

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A Nonrelation Example

EmployeeNumber Phone LastName

100 335-6421,454-9744

Abermany

101 215-7789 Caldera

104 610-9850 Copley

107 299-9090 Jacksoni

Cells of the table hold multiple values

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EmployeeNumber Phone LastName

100 335-6421 Abermany

101 215-7789 Caldera

104 610-9850 Copley

100 335-6421 Abermany

107 299-9090 Jacksoni

No two rows may be identical

A Nonrelation Example

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Terminology

Table Row Column

File or Data file

Record Field

Relation Tuple Attribute

Synonyms…

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A Key and Uniqueness of Keys

• A key is one (or more) columns of a relation that is (are) used to identify a row

Unique Key Non-unique Key• Data value is unique for each row.• Consequently, the key will uniquely identify a row.

• Data value may be shared among several rows.• Consequently, the key will identify a set of rows.

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A Composite Key

• A composite key is a key that contains two or more attributes

• For a key to be unique, often it must become a composite key

• For example, • To identify a family member, you need to

know a FamilyID, a FirstName, and a Suffix (e.g., Jr.)

• The composite key is: (FamilyID, FirstName, Suffix)

• One needs to know the value of all three columns to uniquely identify an individual

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A Candidate and Primary Key

• A candidate key is called “candidate” because it is a candidate to become the primary key

• A candidate key is a unique key• A primary key is a candidate key chosen to

be the main key for the relation• If you know the value of the primary key,

you will be able to uniquely identify a single row

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Relationships Between Tables• A table may be related to other tables

• For example• An Employee works in a Department• A Manager controls a Project

• To preserve relationships, you may need to create a foreign key

• A foreign key is a primary key from one table placed into another table

• The key is called a foreign key in the table that received the key

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Foreign Key Example

Project

ProjID

ProjName

MgrID

Manager

MgrID

MgrName

Foreign Key

Primary Key

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Department

DeptID

DeptName

Location

Employee

EmpID

DeptID

EmpNameForeign Key

Primary Key

Foreign Key Example

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Referential Integrity

• Referential integrity states that every value of a foreign key must match a value of an existing primary key

• For example (see previous slide)• If EmpID = 4 in EMPLOYEE has a

DeptID = 7 (a foreign key), a Department with DeptID = 7 must exist in DEPARTMENT

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Referential Integrity• Another perspective… The value of the Foreign Key

EmployeeID in EQUIPMENT

must exist in

The values of the Primary Key EmployeeID

in EMPLOYEE

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A Surrogate Key• A Surrogate Key is a unique,

numeric value that is added to a relation to serve as the Primary Key

• Surrogate Key values have no meaning to users and are usually hidden in forms, queries and reports

• A Surrogate Key is often used in place of a composite primary key

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Surrogate Key Example• If the Family Member Primary Key is FamilyID,

FirstName, Suffix, it would be easier to append and use a surrogate key of FamMemberID

• FamilyID, FirstName and Suffix remain in the relation

• Referential Integrity:Use… (FamMemberID) in School must exist in

(FamMemberID) in FamilyMemberInstead of:

(FamilyID, FirstName, Suffix) in School must exist in (FamilyID, FirstName, Suffix) in FamilyMember

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Functional Dependency

• A relationship between attributes in which one attribute (or group of attributes) determines the value of another attribute in the same table

• Illustration…• The price of one cookie can determine

the price of a box of 12 cookies

(CookiePrice, Qty) BoxPrice

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Determinants

• The attribute (or attributes) that we use as the starting point (the variable on the left side of the equation) is called a determinant

(CookiePrice, Qty) BoxPrice

Determinant

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Candidate/Primary Keys and Functional Dependency

• By definition…A candidate key of a relation will functionally determine all other attributes in the row

• Likewise, by definition…A primary key of a relation will functionally determine all other attributes in the row

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Primary Key and Functional Dependency Example

(EmployeeID)(EmpLastName, EmpPhone)

(ProjectID) (ProjectName, StartDate)

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Normalization

• Normalization is a process of analyzing a relation to ensure that it is well-formed

• More specifically, if a relation is normalized (well-formed), rows can be inserted, deleted, or modified without creating update anomalies

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Normalization Principles

• Relational design principles for normalized relations:• To be a well-formed relation, every

determinant must be a candidate key• Any relation that is not well formed

should be broken into two or more well-formed relations.

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Normalization Example(StudentID)

(StudentName, DormName, DormCost)

(DormName) (DormCost)

However, if…

(StudentID) (StudentName, DormName)

(DormName) (DormCost)

Then DormCost should be placed into its own relation,resulting in the relations:

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Normalization Example(AttorneyID,ClientID)

(ClientName, MeetingDate, Duration)

(ClientID) (ClientName)

However, if…

(ClientID) (ClientName)

(AttorneyID,ClientID)

(MeetingDate, Duration)

Then ClientName should be placed into its own relation,resulting in the relations:

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Structured Query Language (SQL)

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Structured Query Language

• Structured Query Language• Acronym: SQL• Pronounced as “S-Q-L”• Also pronounced as “Sequel”• Originally developed by IBM as the

SEQUEL language in the 1970s• SQL-92 is an ANSI national standard

adopted in 1992

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SQL Defined

• SQL is an international standard for creating, processing and querying database and their tables.

• SQL is comprised of:• A data definition language (DDL)

• Used to define database structures

• A data manipulation language (DML)• Data definition and updating• Data retrieval (Queries)

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SQL for Data Definition

• The SQL data definition statements include• CREATE

• To create database objects

• ALTER• To modify the structure and/or

characteristics of database objects

• DROP• To delete database objects

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SQL for Data Definition: CREATE

• Creating database tables• The SQL CREATE TABLE statement

CREATE TABLE Employee( EmpID Integer Primary Key, EmpName Char(25) Not Null);

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SQL for Data Definition: CREATE with CONSTRAINT

• Creating database tables with PRIMARY KEY constraints• The SQL CREATE TABLE statement• The SQL CONSTRAINT keyword

CREATE TABLE Employee( EmpID Integer Not Null, EmpName Char(25) Not Null CONSTRAINT EmpPK PRIMARY KEY (EmpID));

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SQL for Data Definition: CREATE with CONSTRAINT

• Creating database tables with composite primary keys using PRIMARY KEY constraints• The SQL CREATE TABLE statement• The SQL CONSTRAINT keyword

CREATE TABLE Emp_Skill ( EmpID Integer Not Null,

SkillID Integer Not Null, SkillLevel Integer, CONSTRAINT EmpSkillPK PRIMARY KEY (EmpID, SkillID)

);

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SQL for Data Definition: CREATE with CONSTRAINT

• Creating database tables using PRIMARY KEY and FOREIGN KEY constraints• The SQL CREATE TABLE statement• The SQL CONSTRAINT keyword

CREATE TABLE Emp_Skill ( EmpID Integer Not Null,

SkillID Integer Not Null,SkillLevel Integer,CONSTRAINT EmpSkillPK PRIMARY KEY (EmpID, SkillID),

CONSTRAINT EmpFK FOREIGN KEY EmpID REFERENCES Employee

(EmpID),CONSTRAINT SkillFK FOREIGN KEY

SkillID REFERENCES Skill (SkillID));

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SQL for Data Definition: CREATE with CONSTRAINT

• Creating database tables using PRIMARY KEY and FOREIGN KEY constraints• The SQL CREATE TABLE statement• The SQL CONSTRAINT keyword• ON UPDATE CASCADE and ON DELETE CASCADE

CREATE TABLE Emp_Skill ( EmpID Integer Not Null,

SkillID Integer Not Null,SkillLevel Integer,CONSTRAINT EmpSkillPK PRIMARY KEY (EmpID, SkillID),

CONSTRAINT EmpFK FOREIGN KEY (EmpID) REFERENCES Employee (EmpID) ON DELETE CASCADE,

CONSTRAINT SkillFK FOREIGN KEY (SkillID) REFERENCES Skill (SkillID)

ON UPDATE CASCADE);

When the row of EmpID (primary key) in Employee TABLE is deleted, the EmpFK (foreign key) is deleted also.

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Deleting Database Objects: DROP

• To remove unwanted database objects from the database, use the SQL DROP statement

• Warning… The DROP statement will permanently remove the object and all data

DROP TABLE Employee;

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Removing a Constraint: ALTER & DROP

• To change the constraints on existing tables, you may need to remove the existing constraints before adding new constraints

ALTER TABLE Employee DROP CONSTRAINT EmpFK;

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SQL for Data Retrieval (Queries)

• SELECT is the best known SQL statement

• SELECT will retrieve information from the database that matches the specified criteria

SELECT EmpName

FROM Emp;

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The Results of a Query is a Relation

• A query pulls information from one or more relations and creates (temporarily) a new relation

• This allows for a query to: • Create a new relation• Feed information to another query

(as a “sub-query”)

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Displaying All Columns: *• To show all of the column values for the

rows that match the specified criteria, use an *

SELECT *

FROM Emp;Showing a Row Only Once: DISTINCT

• A qualifier may be added to the SELECT statement to inhibit duplicate rows from displaying

SELECT DISTINCT DeptID

FROM Emp;

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Specifying Search Criteria: WHERE

• The WHERE clause stipulates the matching criteria for the record that are to be displayed

SELECT EmpName

FROM EmpWHERE DeptID = 15;

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Match Criteria

• The WHERE clause match criteria may include• Equals “=“• Not Equals “<>”• Greater than “>”• Less than “<“• Greater than or Equal to “>=“• Less than or Equal to “<=“

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Match Operators• Multiple matching criteria may be

specified using• AND

• Representing an intersection of the data sets

• OR• Representing a union of the data sets

SELECT EmpNameFROM EmpWHERE DeptID < 7

OR DeptID > 12;

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A List of Values• The WHERE clause may specify that a

particular column value must be included in a list of values

SELECT EmpNameFROM EmpWHERE DeptID IN (4, 8, 9);

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The Logical NOT Operator

• Any criteria statement may be preceded by a NOT operator which is to say that all information will be shown except that information matching the specified criteria

SELECT EmpNameFROM EmpWHERE DeptID NOT IN (4, 8, 9);

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Finding Data Matching a Range of Values: BETWEEN

• SQL provides a BETWEEN statement that allows a user to specify a minimum and maximum value on one line

SELECT EmpNameFROM EmpWHERE SalaryCode BETWEEN 10 AND 45;

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Allowing for Wildcard Searches: LIKE

• Sometimes it may be advantageous to find rows matching a string value using wildcards• Single character wildcard character is

an underscore (_)• Multiple character wildcard character

is a percent sign (%)

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Wildcard Search Examples

SELECT EmpIDFROM EmpWHERE EmpName LIKE ‘Kr%’;

SELECT EmpIDFROM EmpWHERE Phone LIKE ‘616-___-____’;

3 underscores

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Sorting the Results: ORDER BY

• The results may be sorted using the ORDER BY clause

SELECT *FROM EmpORDER BY EmpName;

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Built-in SQL Functions

• SQL provides several built-in functions • COUNT

• Counts the number of rows that match the specified criteria

• MIN• Finds the minimum value for a specific

column for those rows matching the criteria

• MAX• Finds the maximum value for a specific

column for those rows matching the criteria

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Built-in SQL Functions (continued)

• SUM• Calculates the sum for a specific

column for those rows matching the criteria

• AVG• Calculates the numerical average of a

specific column for those rows matching the criteria

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Built-in Function Examples

SELECT COUNT(DISTINCT DeptID)FROM Emp;

SELECT MIN(Hours), MAX(Hours), AVG(Hours)

FROM ProjectWHERE ProjID > 7;

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Providing Subtotals:GROUP BY

• Subtotals may be calculated by using the GROUP BY clause

SELECT DeptID, COUNT(*)FROM EmpGROUP BY DeptIDHAVING Count(*) > 3;

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Retrieving Information from Multiple Tables

• SubQueries• As stated earlier, the result of a query is a

relation. As a result, a query may feed another query. This is called a subquery

• Joins• Another way of combining data is by using

a Join • Join [also called an Inner Join]• Left Outer Join• Right Outer Join

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Subquery

SELECT EmpNameFROM EmpWHERE DeptID in

(SELECT DeptIDFROM Department

WHERE DeptNameLIKE ‘Accounts%’);

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Join

SELECT EmpNameFROM Emp, DepartmentWHERE Emp.DeptID = Department.DeptID

AND Department.DeptName LIKE ‘Account%’;

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Modifying Data using SQL

• Insert• Will add a new row in a table

• Update• Will update the data in a table that

matches the specified criteria

• Delete• Will delete the data in a table that

matches the specified criteria

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Adding Data: INSERT

• To add a row to an existing table, use the INSERT statement

INSERT INTO Emp VALUES (91, ‘Smither’,

12);

INSERT INTO Emp (EmpID, SalaryCode) VALUES (62, 11);

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Changing Data Values: UPDATE

• To change the data values in an existing row (or set of rows) use the Update statement

UPDATE EmpSET Phone =‘791-555-1234’WHERE EmpID = 29;

UPDATE EmpSET DeptID = 44WHERE EmpName LIKE ‘Kr%’;

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Deleting Data: DELETE

• To delete a row or set of rows from a table using the DELETE statement

DELETE FROM EmpWHERE EmpID = 29;

DELETE FROM EmpWHERE EmpName LIKE ‘Kr%’;

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Movie(title, length)

SELECT title AS name, length * 0.016667 AS lengthInHours

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SELECT nameFROM MovieExec, Movies, StarInWHERE cert# = producerC# AND

title = movieTitle ANDyear = movieYear ANDstarName = ‘Harrison Ford’

MovieExec(name, address, cert#, netWorth)Movies(title, year, length, genre, studioName, producerC#)StarsIn(movieTitle, movieYear, starName)

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Movies(title, year, length, genre, studioName, producerC#)MovieExec(name, address, cert#, netWorth)StarsIn(movieTitle, movieYear, starName)

SELECT nameFROM MovieExecWHERE cert# IN

(SELECT producerC#FROM MoviesWHERE (title, year) IN

(SELECT movieTitle, MovieYear)FROM StartsInWHERE starName = ‘Harrison Ford’)

);