# Recent questions tagged candidate-keys

1 vote
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Let $R=(A,B,C,D,E,F)$ be a relation scheme with the following dependencies: $C\to F,E\to a,EC\to D, A\to B$. Which of the following is a key for $R$? $CD$ $EC$ $AE$ $AC$
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The primary key is selected from the: Composite keys Determinants Candidate keys Foreign keys
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If there is more than one key for relation schema in DBMS then each key in relation schema is classified as prime key super key candidate key primary key
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Which one is correct w.r.t. RDBMS? primary key $\subseteq$ super key $\subseteq$ candidate key primary key $\subseteq$ candidate key $\subseteq$ super key super key $\subseteq$ candidate key $\subseteq$ primary key super key $\subseteq$ primary key $\subseteq$ candidate key
1 vote
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Which of the following key constraints is required for functioning of foreign key in the context relational databases? Unique key Primary key Candidate key Check key
1 vote
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In relational database management, which of the following is/are property/properties of candidate key? P: Uniqueness Q: Irreducibility P only Q only Both P and Q Neither P nor Q
1 vote
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Consider the following relation R(A1, A2,...A15) with (A1,A2, ... A6) of relation R are simple candidate key. The number of possible superkey in relation R is_
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I've some elementary doubts regarding Foreign keys (referential integrity) : Can a foreign key consist of a collection of attributes - ie. can two or more columns collectively form a foreign key? If foreign key refers to a column within the same ... that has either: Multiple candidate keys Composite candidate keys Overlapping candidate keys If possible, please provide an example. Thank You.!
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Can Prime attribute be NULL in any of the the Candidate key ?? Can Prime attribute be NULL in Primary key ??
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How many Super keys Possible for R(A,B,C,D,E) with 1. {A,BC,DE} as the keys ? 2. {A,BC,CDE} as the keys ?
1 vote
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An instance of a relational schema R(A,B,C,D) has distinct values for attribute A then A can be 1) candidate key 2)non key 3)super key 4)none
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Referencing to this gate ques- https://gateoverflow.in/16095/gate2004_13-let-and-two-relation-schema-where-the-primary-key Let R1 (A, B, C) and R2 (D, E) be two relation schema, where the primary keys are shown underlined, and let C be a foreign key in R1 ... foreign key, subtracting entities of D from C can still have null and other values(those were duplicate). So, how will it get empty set?
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Relation R(A1, A2, A3 ..... An) n attributes. On this relation m simple candidate key (m ≤ n). How many super keys possible in this relation? A. 2m – 1 B. (2n – 1) ⋅ 2n-m C. 2n – 1 D. (2m – 1) 2n-m One way is by taking instances and solve it, but plz without it what's the logic behind the answer?
1 vote
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R (A1, A2, ….An) and every (n-2) attributes of R forms a candidate key. How many super keys are there in R? a) $_{n-2}^{n}\textrm{C}$ b) $_{n-2}^{n}\textrm{C}$ * 4 c) $_{n-2}^{n}\textrm{C}$ * n d) $_{n-2}^{n}\textrm{C}$ + n +1
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Match the following: List - I 1.Determinants 2.Candidate key 3.Non - redundancy 4.Functional dependency List - II A. No attribute can be added B. Uniquely identified a row C. A constraint between two attribute D. Group of attributes on the left hand side of arrow of function dependency. ... c) 3 4 1 2 d) 4 3 2 1 Ans b) how Non - redundancy and Uniquely identified a row are related ? Thanks :)
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I came across a statement that says that in BCNF, a prime attribute cannot be transitively dependent on a key. But consider a relation R (A, B, C) where, A --> ABC , B --> ABC , C --> ABC Clearly it is in BCNF and each of A, B and C are candidate keys. Now A - ... > C and A --> C . Thus, we can tell C(a prime attribute) is transitively dependent on A (a candidate key) !! Where am I making mistake?
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If A Relation R(A,B,C,D) and CK given is (AB,C) and FD is given as A->C Then the relation is in which highest normal form?
1 vote
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R(A,B,C,D,E,F,G,H) A->BC B->CFH CH->G E->A A->EG what is the number of candidate key
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A relational schema R with attributes (ABCDEFG).It is known that D never appears on RHS of any FD.How many different possibilities are there for what a Candidate key of R can be.?
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Given relation R(A, B, C, D, E) and set of functional dependencies F = {AB → C, AB → D, D → A, BC → D, BC → E} Number of candidate key in the following relation have?
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A relation R(A,B,C,D,E,F) holds following FDs $AB\rightarrow C$ $C\rightarrow D$ $D\rightarrow EA$ $E\rightarrow F$ $F\rightarrow B$ The number of minimal candidate keys of R are _______.
Consider the following database table having A, B, C and D as its four attributes and four possible candidate keys (I, II, III and IV) for this table: A B C D $a_1$ $b_1$ $c_1$ $d_1$ $a_2$ $b_3$ $c_3$ $d_1$ $a_1$ $b_2$ $c_1$ $d_2$ ... not equal to $d_2$) then which of hte above could not be the candidate key for the database table? I nad III only III and IV only II only I only