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## Questions on Super Keys and Candidate Keys## Questions on Super Keys and Candidate Keys using Closure
Identify Super Keys and Candidate keys :
Question 1 : Let R(ABCDE) is a relational schema, where (AB) Solution : AB : Not a Candidate Key, AB is only : Super Key Question 2 : Let R(ABCDE) is a relational Schema having FDs {AB→C, C→D, B→E} Find out the Candidate Key ? Solution : (AB Question 3 : Let R(ABCDE) is a relational schema having FDs {AB→C , C→D, B→EA} Find Out the Candidate Key ? Solution : (AB Question 4 : Let R(ABCDE) is a relational schema having FDs {A→B, B→C, C→D} Find out the Candidate Key ? Solution : (AE Question 5 : Let R(ABCDEF) is a relational schema having FDs {A→BCDEF, BC→ADEF, B→C, D→E} Find out the Candidate Key ? Solution: (A) Question 6: Given the following set F of functional dependencies for relation schema R = {A, B, C, D, E}. {A -> BC, CD -> E, B -> D, E -> A} List the candidate keys for R. Solution : (A) Question 7: Consider a relation R(A,B,C,D,E) with the following dependencies: {AB-> C, CD -> E, DE -> B} Is AB a candidate key of this relation? If not, is ABD? Explain your answer. No. The closure of AB does not give you all of the attributes of the relation. For ABD, (ABD)+ = ABDCE ⇒ Super Key (A) = {A} (B) = {B} (D) = {D} ⇒ ABD is a candidate key. No subset of its attributes is a key. Question 8 : Consider a relation with schema R(A,B,C,D) and FDs {AB -> C, C -> D, D -> A}. What are all candidate keys of R? (AB) |

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