TU Wien:Datenbanksysteme VU (Hose)/Quiz 2 (2024-03-12)
Given R(A, B, C) and S (X, Y, Z) what is the schema for R natural_join S?
- (X, Y, Z)
- (A, B, C, X)
- (C, X, Y, Z)
- (A, B, C)
+ (A, B, C, X, Y, Z)
Given R(A, B, C) and S(A, B, Z) what is the schema for R natural_join S?
- (A, B, C)
- (A, B, Z)
- (R.A, R.B, C, S.A, S.B, Z)
+ (A, B, C, Z)
Given R(A, B, C) and S(A, B, Z) what is the schema for R theta_join S with condition R.A=S.A and R.B=S.B?
- (A, B, C, Z)
- (A, B, C)
- (A, B, Z)
+ (R.A, R.B, C, S.A, S.B, Z)
What is true for R left_outer_join S?
+ The resulting relation may contain null values.
+ The size of the resulting relation |R left_outer_join S| is at least as big as |R natural_join S|.
- It is an illegal relational expression.
- It is the same as S left_outer_join R.
- It is the same as R right_outer_join S.
- It is the same as R full_outer_join S.
Given two relations R(A, B ,C) and S(C, Y, Z) what is the schema for R right_outer_join S?
- (A, B, Y, Z)
- (A, B, C)
+ (A, B, C, Y, Z)
- (C, Y, Z)
Given two relations R(A,B,C) and S(X,Y,A) what is the schema for R left_semi_join S?
- (A, B, C, X, Y)
- (A, X, Y)
- (B, C, X, Y)
+ (A, B, C)
Natural Joins are derived relational operators that use which of the following fundamental operators?
+ projection
+ cartesian product
+ selection
- union
- difference
- rename
Two relations R and S are union compatible if ...
+ for the i-th attribute of R and S they have the same domain.
+ they have the same arity.
- they have at most 10 attributes.
- they have the same number of tuples
- the attribute names of the columns are the same.
Which of the following statements are correct?
+ A valid relation can consist of many tuples.
+ A valid relation has at least one attribute.
- A valid relation can contain duplicate tuples.
- A valid relation can have no more than one attribute.
- A tuple consists of many relations.
Which of the following joins are not commutative?
+ Left outer join
+ Right outer join
+ Semi join
+ Natural join
Are duplicate tuples allowed in the relational model?
False
If the arity of R is 4 and the arity of S is 3, then what is the arity of R x S ?
+ 7
- 1
- 3
- 4
- 12