IT revision notes databases chapter 5 as ocr

summary of part of chapter 5 on databases for as ocr IT

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IT revision notes chapter 5 database
Database
A database is a collection of related data.
Can store lots of data without taking up much space
Users can search, sort and combine data quickly
Used to produce reports
Database terms
Entity
Name given to anything data is stored about
Data held in a certain entity refers to that entity. E.g. the entity customer
only holds data about customers
In a database, entities are the table name
Attributes
Describe the properties of an entity. E.g. attributes for the entity of
customers could be forename, surname, address, phone number.
In a database attributes are the fields
Table
Contain data about a particular entity e.g. students, suppliers, customers
Data is organised in rows (records) and columns (fields).
If the table is to be called a table is must have these features:
Unique name
Each field needs a unique name
Each record needs to be unique
Each data item in a field must contain a single data item
Record
Single row in a table
Collection of data about a single item or event
E.g. a record can be about a individual like a customer
Made up of fields which contain different data types
Each record must be unique
Field
An individual data item in a record
Each field must have a unique name
Should only contain a single data item

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Have individual data types and their own validation
Each field has its own data type
Keys
Primary key
This is a field in a table that allows each record to be uniquely identified
Each value in the primary key must be unique
ID can be a primary key as it has a different value in each record
Names can't be a primary key as they can be the same in 2 or more records
There are 2 types of primary key: simple and compound
Simple…read more

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