SNF, Second Normal Form

Remove part key dependencies

Are any data elements dependent on a part of the FNF key?

  1. Create a new table for these data elements, avobe the old one. Draw a connection between the old and the new table, a many to one relation.
  2. Mark the relation at the many side with a red capital I meaning Identifying.
  3. The new table will get a smaller key. Create new sticky pads for the new key. Keep the key in the old table.
  4. Move the dependent data to the new table.
  5. Repeat these steps for the other part-key dependencies.
Design in SNF, Second Normal Form

Link table

Note: In this old table there is no data anymore. Yet, the combination of keys is meaningful. Such a link table makes a many to many relation possible:
  • One reader can have many subscriptions to various newspapers.
  • One newspaper has many readers with a subscription.
Database design with 2 one-to-many relations This is quite a reasonable database design, with three tables and two one-to many relations. Using the keys you can find related information in the other tables.
  1. Subscription has the tax number.
  2. With the tax number you can read the correct row in "Reader".
  3. In the row of Reader there is oa the house address and the house number.