Set of solved exercises in Normalization / Normalization Solved Examples / How to find candidate keys, and primary keys in database? / Sets of examples to find the keys of a tables / Process of Key finding in a database - Examples
Question:
Consider a relation R(A, B, C, D, E) with FD's AB → C, CD → E, C → A, C → D, D → B.
Determine all the keys of
relation R. Do not list superkeys that are not a candidate key.
Solution:
Key 1:
From above points, we would know
that the attributes AB together can identify all the other attributes of R uniquely.
Hence, AB is one of the keys.
Key 2:
From AB, we can obtain the rest
of the attributes. (See the discussion in Key 1 above). Hence, C is one of the
keys.
Key 3:
From AB, we can obtain the rest
of the attributes. (See the discussion in Key 1 above). Hence AD is one of the
keys.
The keys are AB, AD, and C.
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