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asked in Databases by Boss (6k points)   | 78 views

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Lets take an example, Below are three instances of table with ratio of tuples equal to the original relation.

A B C
 Y  Y  L
 P  Q  M
 C  D  N
 X  Z  O

 

C D E
 L  Z  A
 M  Z  A
 N  Z  A
 L  Z  B
 M  Z  B
 O  Z  B

 

E F
 A  Z
 B  Z

If we join tem in any way the resulting table will have 6 tuples 
We can thus conclude that P join Q join R will result in 300 tuples.

A B C D E F
 Y  Y  L  Z  A  Z
 Y  Y  L  Z  B  Z
 P  Q  M  Z  A  Z
 P  Q  M  Z  B  Z
 C  D  N  Z  A  Z
 X  Z  O  Z  B  Z

 

answered by Active (2.1k points)  
selected by
@Vijay. I dont think that for relation Q, one of C or E can be null.
I thought, C in Q is foreign key pointng to C in P and similarly E in Q referring to E in R.

So, we should not consider foreign key even if there is common attribute between two relation unless it is mentioned explicitly. ??
@Vijay. Yes. We shouldn't consider unless explicitly stated because we have satisfied the conditions they have given.
But, if options are given, we need to consider that C is foreign key in Q   :P
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