Consider the following set of functional dependencies on the schema (A, B, C)
A --> BC,
B —> C,
A —> B,
AB —> C
The cannonical cover for this set is
A. | A —> BC and B ---->C |
B. | A ----> BC and AB —> C |
C. | A —> BC and A —> B |
D. | A —> B and B —> C |
Option: A Explanation : Sets of functional dependencies may have redundant dependencies that can be inferred from the other functional dependencies. A canonical cover of F is a “minimal” set of functional dependencies equivalent to F, having no redundant dependencies or redundant parts of dependencies. As we can infer all FD's from option A , so A is right answer. Click on Discuss to view users comments. |
A table T1 in a relation database has following rows and columns.
Roll number Marks.
1 10
2 20
3 30
4 NULL
The following sequence of SQL statements was successfully executed in table T1.
Update T1 set marks =marks + 5 ;
select avg(marks) from T1 ;
What is the output of the select statement?
A. | 18.75 |
B. | 20 |
C. | 25 |
D. | NULL |
Option: A Explanation : Average = (15+25+35+null)/4 = 18.75 Click on Discuss to view users comments. kiran said: (3:45pm on Sunday 12th May 2013)
5 in each marks then calculate and find its average
mubina said: (3:44pm on Thursday 27th June 2013)
null is updated but the average calculated on (15 25 35)/3 so it wwill give output 25
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Which normal form is considered adequate for relational database design?
A. | 2NF |
B. | 3NF |
C. | 4 NF |
D. | BCNF |
Option: B Explanation : Click on Discuss to view users comments. |
A functional dependency of the form x —> y is trival if
A. | y ⊆ x |
B. | y ⊂ x |
C. | x ⊂ y |
D. | x ⊂y and y⊂ x |
Option: A Explanation : Click on Discuss to view users comments. |
If every non-key attribute is functionally depedent primary key, then the relation will be in
A. | First normal form |
B. | Second normal form |
C. | Third form |
D. | Fourth normal form |
Option: B Explanation : Click on Discuss to view users comments. Amit said: (1:15pm on Friday 6th September 2013)
in 2nf partial dependency should not exist den how it can be 2nf
Atul said: (10:56pm on Wednesday 11th January 2017)
I think it should be A. First normal form , i.e for 2nf there would be FULLY functionally dependent..
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