The Gateway to Computer Science Excellence
First time here? Checkout the FAQ!
x
+20 votes
5.1k views

Consider the join of a relation $R$ with a relation $S$. If $R$ has $m$ tuples and $S$ has $n$ tuples then the maximum and minimum sizes of the join respectively are

  1. $m+n$ and $0$
  2. $mn$ and $0$
  3. $m+n$ and $|m-n|$
  4. $mn$ and $m+n$
asked in Databases by Veteran (59.6k points)
edited by | 5.1k views
–4
ans plz

1 Answer

+32 votes
Best answer

Answer is B.

$mn$
Case 1: if there is a common attribute between $R$ and $S$, and every row of $r$ matches with the each row of $s$- i.e., it means, the join attribute has the same value in all the rows of both $r$ and $s$,
Case 2: If there is no common attribute between $R$ and $S.$

$0$ There is a common attribute between $R$ and $S$ and nothing matches- the join attribute in $r$ and $s$ have no common value.

answered by Loyal (8.1k points)
edited by
+7
mn occurs during cartesian product of two relation ....

and 0 occurs during natural join of two realtion(In best case )....
+26
^
Join means Natural Join only.
Natural Join gives result as cartesian product if no attribute is matching in both relations.
eg- $R(A,B)$ and $S(C,D)$

Natural Join gives result as empty relation  if  at least one of the attribute matches but value does not matches.
$\begin{tabular}{ |c|c| }

\hline \multicolumn{2}{|c|}{R} \\

\hline A & B \\

\hline a1 & b1 \\

a2 & b2

\\ a3 & b3 \\

\hline

\end{tabular}$

$\begin{tabular}{ |c|c| }

\hline \multicolumn{2}{|c|}{S} \\

\hline B & C \\

\hline b3 & c1 \\

b4 & c2 \\

b5 & c3 \\

\hline \end{tabular}$

In this case $R \Join S$ is empty.
0
Thanks @Sachin it  more clear now.
0
sachin sir shukriya


Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true

40,903 questions
47,558 answers
146,290 comments
62,306 users