GATE CSE 2024 | Set 1 | Question: 25

Question

Consider the following two relations, $R(A, B)$ and $S(A, C)$:

$R$
$A$	$B$
$10$	$20$
$20$	$30$
$30$	$40$
$30$	$50$
$50$	$95$

$S$
$A$	$C$
$10$	$90$
$30$	$45$
$40$	$80$

The total number of tuples obtained by evaluating the following expression

$\sigma_{B<C}\left(R \bowtie_{R . A=S . A} S\right)$ is ___________.

Answer 1

The output of $R( \bowtie_{R.A=S.A} S)$ is simply return the number of tuples where $R.A$ value is equal to $S.A$. So the output is as follow:

A	B	C
10	20	90
30	40	45
30	50	45

from the above table now we have to perform $(\sigma_{B<C}(R \bowtie_{R.A=S.A} S))$. it return the number of rows where $B's$ value is less than $C$. so the output is:

A	B	C
10	20	90
30	40	45

 

So the given expression returns $2$ tuples as output.