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first form normalizations and second form normalization

    Question

  • Hi everyone,
    What is the main difference between first form normalizations and second form normalization ?
    In my opinion, they are both generated for the same operation which is to prevent redundancy(in other words; duplication of data in several records).
    So would you please explain it to me ?

    Thanks
    Wednesday, July 19, 2006 3:15 PM

Answers

  • Taken from: http://databases.about.com/od/specificproducts/a/normalization.htm

    First normal form (1NF) sets the very basic rules for an organized database:

    • Eliminate duplicative columns from the same table.
    • Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
    Second normal form (2NF) further addresses the concept of removing duplicative data:
    • Meet all the requirements of the first normal form.
    • Remove subsets of data that apply to multiple rows of a table and place them in separate tables.
    • Create relationships between these new tables and their predecessors through the use of foreign keys.

     

    In Essence:

    1NF: If you have a table of users that stores their addresses, you don't want to have their addresses (street, city, state, etc) listed twice; i.e. their shipping and billing addresses are the same. So, move addresses to their own table and link with foreign keys. This reduces duplicate data PER ROW.

    2NF: States can be repeated through rows, i.e. two people live in California. So,  remove states from the addresses table and create a states table. Link addresses to states with foreign keys. This reduces duplicate data PER COLUMN.

    Wednesday, July 19, 2006 5:47 PM