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Databases and Data Representation

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Databases and Data Representation

Database Management System (DBMS) Provides efficient, convenient, and safe multi-

user storage of and access to massive amounts of persistent data

Provides a programming interface that allows a user or program too - Create new databases and specify their structureo - Query and modify the data

Early DBMSs were ad hoc, with no two the same Now one approach predominates: relational

databases and SQL (Structured Query Language)

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Databases

A "relation" is a table of data

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4 Josh CS120-02 23

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Databases

The columns are known as "attributes"

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LectID Name Course Students

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Databases

The rows are called "tuples"

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LectID Name Course Students

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Databases

It is allowable for some values to be missing

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LectID Name Course Students

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Databases

We can add, remove, or update tuples

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LectID Name Course Students

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Databases

Each attribute has an underlying domain, or data type

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LectID Name Course Students

int string string int

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Databases

The structure of the table is referred to as its schemao Lecturers(LectID, Name, Course, Students)

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LectID Name Course Students

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Primary Key

Every table must have a primary keyo No two tuples can have the same LectID

o LectID cannot be null

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LectID Name Course Students

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Tables

Suppose that we want to add data about lecturers offices

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Name Course StudentsLectID

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Tables

But suppose that lecturers can have more than one office.

We can’t add additional rows for the same lecturers without violating the primary key constraint, so we use another table.

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Name Course StudentsLectID Building Room

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Multiple Tables

Solution: Add a new table

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Name Course StudentsLectID

Shereen Strain 203C

Josh Marsh 324

Josh Strain 202

Doug Strain 201

Building Room

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Relationships

Better to store LectID

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Name Course StudentsLectID

1 Strain 203C

4 Marsh 324

4 Strain 202

2 Strain 201

Building RoomLectID

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Relationships

Better to store LectID

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2 Doug CS300-01 11

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5 Mike CS120-02 19

Name Course StudentsLectID

1 1 Strain 203C

2 4 Marsh 324

3 4 Strain 202

4 2 Strain 201

Building RoomLectID

Foreign key

Primary key

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SQL Queries

SELECT returns tuples that satisfy some condition

SELECT Name, Course FROM Lecturers WHERE Students > 15

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Name Course StudentsLectID

Josh CS120-02

Mike CS120-01

Name Course

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SQL Queries

SELECT *

FROM Lecturers

WHERE Students > 15

Attributes

Relations

Tuples

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SQL Queries

SELECT *

FROM Lecturers

WHERE Students > 15

OR Name = ‘Shereen’

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SQL Queries

Wildcards:o % matches any number of characters

o _ matches any single character

o [] matches any single character in set or range

o [^] matches any single character not in set or range

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Database Management Systems

Many examples of DBMSso Oracle

o SQL Server

o MySQL http://dev.mysql.com/