Relational databases

A uses tables to store data in the database. Each of these tables corresponds to an entity (anything about which we need to store data, like a person, place or thing).

Relationships are created between tables using key fields. Relationships can be classified as ONE to ONE, ONE to MANY, MANY to ONE and MANY to MANY.

Data types

A record structure allows for multiple different types of data to be stored. For example, a simple database may hold your name as text, your age as a number and your gender as a Boolean value (Male | Female).

Common data types utilised in databases are listed below:

Data type	Description	Example data
Number/integer	These are whole numbers only	Age = 16
Real/float	These are numbers that can have a decimal part	0.1, 1.2, 3.4, 6.0
Boolean	This has two values only, true and false	True/False, 1/0, Y/N
Character	This is a single letter, number or symbol	A, B, C, @, *
Text/string	This is used for text, and can include any character	Digital Technology
Date/time	Used for dates and times	29/11/2016 20:55
Calculated	A formula to work something out	Age: Current date minus date of birth

Data type	Number/integer
Description	These are whole numbers only
Example data	Age = 16

Data type	Real/float
Description	These are numbers that can have a decimal part
Example data	0.1, 1.2, 3.4, 6.0

Data type	Boolean
Description	This has two values only, true and false
Example data	True/False, 1/0, Y/N

Data type	Character
Description	This is a single letter, number or symbol
Example data	A, B, C, @, *

Data type	Text/string
Description	This is used for text, and can include any character
Example data	Digital Technology

Data type	Date/time
Description	Used for dates and times
Example data	29/11/2016 20:55

Data type	Calculated
Description	A formula to work something out
Example data	Age: Current date minus date of birth

��ý

Database applications - CCEARelational databases