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Flip to reveal answersWhat is a functional dependency?
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Question
What is a functional dependency?
Answer
One column's value determining another's. Knowing a StudentID tells you the student's name, so Name is functionally dependent on StudentID. Normal forms are rules about which dependencies are allowed where.
Question
What do 1NF, 2NF and 3NF each require?
Answer
1NF: every cell holds one value and every row is uniquely identified. 2NF: no non-key column depends on only part of a composite key. 3NF: no non-key column determines another non-key column.
Question
What is a partial-key dependency?
Answer
A non-key column depending on only part of a composite primary key. With a key of StudentID and Club, StudentName depends on StudentID alone. It can only arise when the key is composite.
Question
What is a transitive dependency?
Answer
A non-key column determining another non-key column. Club determines Teacher and Teacher determines Room, so Room depends on Club only indirectly — which breaks 3NF.
Question
Why normalise, beyond saving space?
Answer
To prevent update problems, where one copy of a repeated fact is changed and others are not; insert problems, where a new club with no members has nowhere to live; and delete problems, where removing the last member loses the club's details too.
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Database design
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