1
GATE CSE 1999
MCQ (Single Correct Answer)
+1
-0.3

The relational algebra expression equivalent to the following tuple calculus expression:

$$\left\{ {t|t \in r \wedge \left( {t\left[ A \right] = 10 \wedge t\left[ B \right] = 20} \right)} \right\}$$ is:
A
$${\sigma _{\left( {A = 10 \vee B = 20} \right)}}\left( r \right)$$
B
$${\sigma _{\left( {A = 10} \right)}}\left( r \right) \cup {\sigma _{\left( {B = 20} \right)}}\left( r \right)$$
C
$${\sigma _{\left( {A = 10} \right)}}\left( r \right) \cap {\sigma _{\left( {B = 20} \right)}}\left( r \right)$$
D
$${\sigma _{\left( {A = 10} \right)}}\left( r \right) - {\sigma _{\left( {B = 20} \right)}}\left( r \right)$$
2
GATE CSE 1994
True or False
+1
-0
Give a relational algebra expression using only the minimum number of operators from $$\left( { \cup ,\, - } \right)$$ which is equivalent to $$R \cap S$$.
A
TRUE
B
FALSE
3
GATE CSE 1994
True or False
+1
-0
An instance of a relational scheme R(A, B, C) has distinct values for attribute A. Can you conclude that A is a candidate key for R?
A
TRUE
B
FALSE
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