Transcript Relational Databases

28 Database Theory
28 Database Theory
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Our world depends on databases
Google basically IS a database (index)
Facebook is build around databases
So is e-Bay & Netflix and X-Box Live
Travel agents, schools, doctors and
hospitals all rely on them
• You get the idea!
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• Databases are so useful because they’re
so good at storing info
• But they do it in a very structured way
• That’s so the data can also be sorted
• And so the data can also be searched
• So overall, what makes databases so
special is how they store, sort & search
• Let’s look at some examples…
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Store
Search
Sort
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We’re actually going to look at databases
into two stages.
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First, we’ll learn the basics of how
databases work:
A Database Tables
B Types of Data
C Relational Databases
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A Database Tables
• So we’ve said what makes databases so
special is how they store, sort & search
• But how can they do that?
• The secret is that they work in a very
structured or organised way
• This starts with the way that all data is
stored in what are called tables…
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A Database Tables
Here’s a database table for members of a club...
Table
Field name
Record
Field
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A Database Tables
Here’s a database table for members of a club...
Table
Field name
Record
Field
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A Database Tables
Here’s a database table for members of a club...
Table
Field name
Record
Primary Key
Field
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A Database Tables
Recap
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Databases store info in a structured way
Data in a database is stored in a table
Each row is called a record
Each column is called a field
A special field called the primary key
holds a unique identifier for each record
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Database
Theory are everywhere!
‘Unique
identifiers’
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A Database Tables
Recap
Table
All this data is stored in a ??
This is a
??
Field
This is a
??
Recordl
This is the
??
Primary
Key
This is a
??
Field
name
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A Database Tables
Recap
This table has ____
4
records
There are ____
4 fields
The primary key is called LessonID
_______
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A Database Tables
B Types of Data
C Relational Databases
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B Types of Data
• A second secret to how databases
work is the way they handle different
types of data
• Let’s look at an example…
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B Types of Data
Can you spot the different types of data?
We call these ‘data types’
Text
Numbers
Dates
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B Types of Data
• Database tables can store different
data types, such as...
– Text
– Numbers
– Dates
• When building a database, you say
what type of data can go in each field
• This can help prevent errors, such as
checking that dates are DD/MM/YY
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A Database Tables
B Types of Data
C Relational Databases
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C Relational Databases
• Simple databases with just one data table
are called flat file databases.
• But using only one table creates BIG
problems for larger systems because lots of
data can be duplicated and the database
becomes very inefficient.
• So advanced databases use multiple tables
• They are called relational databases
• Let’s look at why they are needed…
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C Relational Databases
• Notice that several patients see Dr Brown
• So her details are duplicated.
• This is called redundant data because copies are
inefficient & cause inconsistencies
• Can you spot one?
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C Relational Databases
PatientID
Primary
Key
DocID
Primary Key
DocID
Foreign Key
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C Relational Databases
We show this relationship in a diagram
Doctors
Patients
DocID
Surname
Department
Mobile
Patient ID
Forename
Surname
DocID
It’s a ‘One To Many’ relationship
One doctor can treat many patients
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C Relational Databases
Car Club
• Again, data is duplicated or redundant
• Redundant data causes inconsistencies
• Can you spot one?
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C Relational Databases
Car Club
SupplierID
1
2
3
1
1
2
SupplierID
1
2
3
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C Relational Databases
We show this relationship in a diagram
Supplier
Member
SupplierID
CarSupplier
Address1
Town
Postcode
MemberID
Forename
Surname
Car Reg
Car Supplier
It’s a ‘One To Many’ relationship
One Car Supplier can supply many members
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C Relational Databases
Dog Kennel Business
• Again, data is duplicated or redundant
• Redundant data causes inconsistencies
• Can you spot any?
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C Relational Databases
Dog Kennel Business
VetID
3
1
2
2
3
2
VetID
1
2
3
Betta Vetz
Top Vets
West Vets
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C Relational Databases
We show this relationship in a diagram
Vet
Pets
VetID
VetName
Address1
Town
Postcode
PetID
Name
Owner Name
Owner Mobile
Vet ID
It’s a ‘One To Many’ relationship
One Car Supplier can supply many members
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