DATABASES

A database is a structured collection of records.

We use it to:
-add, remove, update records
-retrieve data that match certain criteria
-cross-reference data in different tables
-perform complex aggregate calculation

Data bases are use to store data that has any relation (books: author, themes, genre, editions...)

Databases consist of colums and rows (records).



Relational databases:

A relational database is a digital database whose organization is based on the relational model of data, as proposed by E. F. Codd in 1970. The various software systems used to maintain relational databases are known as a relational database management system (RDBMS).

• Primary key / Unique key:

A primary key uniquely specifies a list of ordered elements within a table. In order for an attribute to be a good primary key it must not repeat. 

• Foreign key:

A foreign key is a field in a relational table that matches the primary key column of another table.