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Calculate Super Key
Q1. Let R (ABCD) how many Super Key? With only CK = A
Answer:
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Where A is the candidate key and we can get the super key by the combination of other non – key with the candidate key then B should include with A or not included. So, every non – key has two choices included or non – included, with the candidate key (A).
Smallest Super Key = A (not included any non – key)
Largest super Key = ABCD (included all non – key)
Total number of all super key – 8
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Q2. Let R (ABCD) how many Super Key? With only CK = A and B
This is the same as the above question but in this case, the candidate keys are two A and B.
Now we first calculate how many super keys possible when the candidate is A:
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If we choose B as a candidate key i.e. CK = B
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And super key is
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From both A as CK and B as CK we got 8 + 8 = 16 super key but some of SK is common to both of them like AB = BA, ABD = BAD, ABC = BAC, ABCD = BACD.
4 are common. So, the total number of distinct super key
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How we got because if AB is common we got 2 options.
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So, the total number of the super key by using candidate key A and B
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Q3. Let R (ABCD) how many Super Key? With only Candidate Key = A, B, C
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Now as per the formula total number of super key possible:
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Total number of SK
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Q4. R (A, B, C, D) how many Super Key? Where candidate key = AB, CD
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Q5. R (A, B, C, D) how many Super Key? With only Candidate Key = AB, BD
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Q6. R (ABCDE) How many super keys possible where candidate key = AB, A.
Calculate super key when the candidate is AB and A.
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But we can’t get 16 super keys because here the question is wrong. Because AB, A two candidates never possible, Candidate is minimal key if A is CK then AB is CK not possible.
