data Normalisation

notes on the the different rules that indicate the type of normal form

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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)
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1st normal form

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
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atomic data

  • 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
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2nd normal form

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
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3rd normal form

2 rules

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