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Study Stuff for MCA Examinations - NIMCET
Study Stuff for MCA Examinations - NIMCET
Previous Year Question (PYQs)
Consider a relational schema
$S=(U,V,W,X,Y,Z)$
on which the following functional dependencies hold:
$\{U\to V,\ VW\to X,\ Y\to W,\ X\to U\}$
Which are the candidate keys among following options?
$S=(U,V,W,X,Y,Z)$
on which the following functional dependencies hold:
$\{U\to V,\ VW\to X,\ Y\to W,\ X\to U\}$
Which are the candidate keys among following options?
Solution
Attributes $Y$ and $Z$ are not present on RHS of any FD.So, every candidate key must contain $Y$ and $Z$.
Now check:
$(UYZ)^+=\{U,Y,Z,V,W,X\}$, so $UYZ$ is a key.
$(VYZ)^+=\{V,Y,Z,W,X,U\}$, so $VYZ$ is a key.
$(XYZ)^+=\{X,Y,Z,U,V,W\}$, so $XYZ$ is a key.
Thus, candidate keys are:
$UYZ,\ VYZ,\ XYZ$
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