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Flip to reveal answersWhat are the four steps to normalise a design to 3NF?
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All 5 Flashcards — Normalising to 3NF
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Question
What are the four steps to normalise a design to 3NF?
Answer
List every piece of data with sample rows; make cells atomic and choose the key; move out anything depending on part of a composite key; move out any non-key column determined by another non-key column.
Question
Why write sample rows before normalising?
Answer
Because functional dependencies are far easier to see in actual data than in a list of column names — repeated values make the repeated facts visible.
Question
How do you find a transitive dependency?
Answer
In each table ask whether any non-key column determines another non-key column. If so, both move to a new table, and the determining column stays behind as a foreign key.
Question
How do you check a finished 3NF design?
Answer
Pick a fact the scenario needs and follow the keys to find it. If you cannot reach it, a link is missing; if you find it in two places, the design is not yet in 3NF.
Question
How many tables should a typical scenario produce?
Answer
More than feels natural — a scenario with eight columns usually becomes about four tables. Finishing with one or two almost always means a transitive dependency was missed.
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Topic 3.2 hub
Database design
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