Free Keys, ER and normalization lessonsKeys, ER and normalization · Stage 1 · Modelling the real world · Step 2
From ER model to tables
Map entities, one-to-many, many-to-many and weak entities onto tables, keys and foreign keys. About 13 minutes.
A person can have several phone numbers. Which table design stores this without repeating the person's other data?
- AA phone table with person_id and number, one row per number
- BColumns phone1, phone2, phone3 in person
- COne column holding the numbers separated by commas
Show the answer
A phone table with person_id and number, one row per number. A multi-valued attribute becomes a table of its own.
4 questions on this idea
Short questions that apply the idea to new cases: trace it, work out a number, put steps in order. A wrong answer explains itself.
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