Referential Integrity

Question

Consider the join of a relation R with a relation S. If R has 100 tuples and S has 9 tuples then the maximum and minimum sizes of the join respectively under referential integrity constraint:-

(A) 9 and 0

(B) 9 and 9

(C) 9+100 and 0

(D) 9*100 and 9

Comments

I think having a key is must for a DBMS table.If you have one attribute and that too only foreign key.Then there is no key on the table.Then is it a valid scenario?

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Yes it is. Then that table is totally dependent on its parent table. And that entity will be known as weak entity.

And then that weak entity will form a key using parent's PK with its own foreign key attribute.

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One will be prime key from R, and one will be forign key from S.
 

But if you consider it other way...prime key from S and foreign key from R. 

Then We will get 100 tuples.

Any specific rules to consider while calculating maximum scenario

Answer 1

1. To get the maximum 

assume Referencing Table(table having foreign key, referencing an attribute in relation S) as  R (with 100 tuples)

assume Referenced Table as S(with 9 tuples)

then maximum will be 100 for join on referential integrity constrainst

this will happen when the there is no null values in R for referencing attribute(then every the tuple will be joined with the corresponding matching tuple in the relation S).

hence maximum is 100

2. we get the minimum number of  tuples on join  when for all the tuples referencing attribute is NULL in 

referencing relation. 

then there will be no tuples on  join 

hence minimum will be 0

correct me if am wrong.