Normalisation is the process of organising data into tables so that the results of using the database are unambiguous and as intended.
It is a refinement process that aims to reduce data redundancy.
Normalisation results in a database that is more efficient but more complex because data is separated into more tables.
For example, Table 2.2 is used to keep track of customer purchases and the price of the products.
If you deleted a customer, you would also delete a price.
Normalising would solve this problem by dividing this table into two tables: a table about each customer and a product they had bought and a table about each product and its price.
Making additions or deletions to either table would not affect the other using the database are unambiguous and as intended.
It is a refinement process that aims to reduce data redundancy.
Summary
1st Normal Form (1NF)
Each field contains a single data item - all data values are atomic
e.g. Customer Name becomes Customer First Name and Customer Last Name
or Address is split out into component bits
There can be no multiple items in a single record - no repeating groups
If there are repetitions, then strip the repeating parts out into another table and link it back to the original table.
For each table (incuding new ones created by this step)
Each field has a unique name
It has a primary key
1NF
2nd Normal Form (2NF)
Must be 1NF, plus....
Every non-prime (non-key) attribute of the table is dependent on the whole of every candidate key, i.e. all parts of the primary key.
That is, every column depends on the entire primary key.
What is a Non Key Attribute?
A KEY ATTRIBUTE is one which is a PRIMARY KEY or part of a COMPOSITE PRIMARY KEY
So, therefore, the NON-KEY ATTRIBUTES in a table are the other attributes in the table (i.e. those that aren't a primary key or part of a composite primary key.)
SO...if a table has NO composite primary key, then it is therefore already in 2NF
plus, as a reminder (especially if you are splitting a table into smaller parts, then for each table):
Each field has a unique name
It has a primary key field
2NF
3rd Normal Form (3NF)
Must be 2NF, plus....
All non-key attributes are not dependent on any other non-key attributes
