Joins

Question

Consider the relation r1(P,Q,R) and r2(R,U,V) with primary keys R and U respectively.The relation r1 contains 1500 tuples and r2 contains 2000 tuples.The max size of the join r1  join  is

Comments

What if second relation has redundant tuples based on R attribute?

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@saxena0612

2000 is Max size. What if minimum asked?

I guess 2000 is also minimum

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yes , minimum also would be 2000

Answer 1

Since attribute R is the primary key in R1, it should contain unique values assume 1, 2, 3, 4 .........1499, 1500 (1500 tuples)

There is no constraint on attribute R in R2, it can contain duplicate values assume 1, 1, 1 ...... upto last tuple (2000 tuples) 

If we take natural join of R1 and R2, entry 1 under R (R1 table) matches with 2000 values of 1 under R (R2 table).

Hence maximum 2000 tuples present in natural join

Comments

so join is based on the common attribute R??

i considered as the join is based on attribute R in r1 and attribute U in r2 as they are the primary keys

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Yes... Natural join is possible if there is at least one common attribute that exists between two relation. Also the attribute must have same name and domain.

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So whenever a natural join is performed...the largest tuple value will be the maximum in any case??