Section 7 - Relational databases and SQL

The concept of a database

All databases contain one or more tables

Each record (row) has several fields ( column )

A record can also have a unique identifier known as the primary key, no two records can have the same primary key.

The concept of a relational database

In a relational database, several tables are linked by a common field. The reason we do this instead of one big table is to minimise errors and not have the same piece of data appearing more than once. 

A table can use another table's primary key as a foreign key. This links the two tables together.

There are several ways 2 tables can be connected for example it can be

A one to one relationship (eg headmaster and school)

A one to many relationship (eg pond and fish )

A many to many relationship ( eg…