1
GATE CSE 2021 Set 1
Numerical
+2
-0.67

A relation r(A, B) in a relational database has 1200 tuples. The attribute A has integer values ranging from 6 to 20, and the attribute B has integer values ranging from 1 to 20. Assume that the attributes A and B are independently distributed. The estimated number of tuples in the output of σ(A>10)∨(B=18)(r) is ______

2
GATE CSE 2019
Numerical
+2
-0.67
Consider the following relations P(X,Y,Z), Q(X,Y,T) and R(Y,V).

How many tuples will be returned by the following relational algebra query?
3
GATE CSE 2018
+2
-0.6
Consider the relations $$r(A, B)$$ and $$s(B, C),$$ where $$s.B$$ is a primary key and $$r.B$$ is a foreign key referencing $$s.B.$$ Consider the query

$$Q:$$ $$\,\,\,\,\,\,\,\,\,$$ $$r$$ $$\,\,\,\,$$ $$\bowtie$$ $$\,\,\,\,$$ $$\left( {{\sigma _{b < 5}}\left( s \right)} \right)$$

Let $$LOJ$$ denote the natural left outer-join operation. Assume that $$r$$ and $$s$$ contain no null values.

Which one of the following queries is NOT equivalent to $$Q$$?

A
$${\sigma _{B < 5}}\left( {r\,\,} \right.$$ $$\bowtie$$ $$\left. {\,\,s} \right)$$
B
$${\sigma _{B < 5}}\left( {r\,\,LOJ\,\,s} \right)$$
C
$$r\,\,LOJ\,\,\left( {{\sigma _{B < 5}}\left( s \right)} \right)$$
D
$${\sigma _{B < 5}}\left( r \right)LOJ\,\,s$$
4
GATE CSE 2015 Set 2
+2
-0.6
Consider two relations $${R_1}\left( {A,B} \right)$$ with the tuples $$(1,5), (3,7)$$ and $${R_2}\left( {A,C} \right) = \left( {1,7} \right),\left( {4,9} \right).$$
Assume that $$R(A,B,C)$$ is the full natural outer join of $${R_1}$$ and $${R_2}$$. Consider the following tuples of the form $$(A,B,C): a = (1,5,null),$$ $$b = (1,null,7),$$ $$c = (3, null, 9),$$ $$d = (4,7,null),$$ $$e = (1,5,7),$$ $$f = (3,7,null),$$ $$g = (4,null,9).$$ Which one of the following statements is correct?
A
$$R$$ contains $$a, b, e, f, g$$ but not $$c, d.$$
B
$$R$$ contains all of $$a, b, c, d, e, f, g.$$
C
$$R$$ contains $$e, f, g$$ but not $$a, b.$$
D
$$R$$ contains $$e$$ but not $$f, g.$$
GATE CSE Subjects
EXAM MAP
Medical
NEET