data Normalisation

using a set of rules to make our tables in the database more efficient.

3 stages of normalisation:

• 1st normal form (1NF)
• 2nd normal form (2NF)
• 3rd normal form (3NF)

1st stage of making database efficient

4 rules:

• no columns of repeated data
• each data item is atomic (more on next card about this)
• each row is unique (this is due to the primary key)
• each field has a unique name e.g. 2 fields cannot both be called colour

• data which has been broken down into the smallest units possible without losing the meaning or it
• for example: address can be broken down into address 1, address 2, address 3 and postcode

2 rules

• must be in 1st normal form
• all the key fields must depend on the primary key field
• e.g. fields called first name, second name all depend on the primary key with is called ID

2 rules

• tables must be in 2nd normal form
• no attribute (field) should depend on any other non key attributes