Structures and links (database)

Question 1

What is a rational database?

Answer 1

A relational database will contain at least two tables. In a relational database the tables are linked using key fields.

Question 2

Why are rational databases used?

Answer 2

1) Details need only be entered into the appropriate table in the database once
2) Duplication is avoided – data entered in one table can be shared by other tables. This reduces the potential size of the database file.

Question 3

What is a primary key?

Answer 3

The primary key of a table within a relational database is a field which uniquely identifies each record in the table

Question 4

What is a one-to-one relationship?

Answer 4

One-to-one relationships occur when there is a direct one to one link between data held on two different tables. e..g. National insurance no. and a pupil

Question 5

What is a one-to-many relationship?

Answer 5

One-to-many relationships exist where one instance of an entity can exist lots of times in another entity.

Question 6

Give an example of a many-to-many relationship.

Answer 6

Clubs can accommodate many pupils and pupils can attend many clubs. This is an example of a many-to-many relationship.