Free Keys, ER and normalization lessonsKeys, ER and normalization · Stage 0 · Relations and keys · Step 1
Relations and keys
What a relation is, and how super keys, candidate keys, primary keys and foreign keys pin down rows and tie tables together. About 14 minutes.
A table has attributes (A, B, C), and {A} is a candidate key. Which set is a super key but not a candidate key?
- A{A, B}
- B{A}
- C{B}
Show the answer
{A, B}. It contains the key {A}, so it is unique, but removing B still leaves a key: not minimal.
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