What is the difference between a primary key and a superkey in a …
2014年7月20日 · A superkey of a table T is a set of columns that functionally determines every attribute. A candidate key (CK) is a superkey that contains no smaller superkey. We can pick …
schema - Candidate key = Key = Minimal Superkey? - Database ...
2013年5月17日 · superkey: a set of attributes which will uniquely identify each tuple in a relation. candidate key: a minimal superkey. primary key: a chosen candidate key. secondary key: all …
database design - Functional Dependency and Superkey
2017年1月5日 · For a relation R, FD X->Y, holds true for relation R if and only if whenever two tuples of R have the same value of X, they also have the same value for Y. X and Y are a …
normalization - Superkeys of this relation - Database …
2015年5月9日 · I am trying to find the superkeys of this relation, but I am having troubles finding out how many superkeys there are and exactly what they are. I figured out that the candidate …
relational theory - Database Administrators Stack Exchange
A superkey (and therefore a candidate key) that does not contain all attributes must contain at least an attribute set that is the left side of a functional dependency. Otherwise it would not be …
If A and B are candidate keys, then AB is candidate key or not
2015年1月28日 · The union between A and B is a superkey. (A candidate key is a superkey but a superkey could be not a candidate key) Moreover, remember that a candidate key is a …
normalization - Check if relation is in BCNF - Database …
I got this result by trying out the combinations DA, DB, DC, DE and finding that only DE is the superkey. I'm curious whether my way to directly check if this relation is in BCNF is correct (I …
normalization - How is every binary relation BCNF? - Database ...
2015年11月1日 · A relation is in BCNF when, for all FDs that apply to the relation, the left hand side is a superkey. That is, it has to contain all the attributes of at least one key. Your relation …
database design - If my understanding of BCNF is correct, how did …
And it is easy to see that D E → A violates the BCNF since D E is not a superkey of the relation, so that now R1 must be decomposed. So, the answer to your question is: The algorithm …
Does 3NF require 2NF? - Database Administrators Stack Exchange
A relation schema R is in third normal form (3NF) if, whenever a nontrivial functional dependency X→A holds in R, either (a) X is a superkey of R, or (b) A is a prime attribute of R. After reading …