Relation between Intersection and natural inner join on common column

Question

 When , then the cost of computing  is

(A)   the same as R  S       

(B)   greater the R  S

(C)    less than R  S                               

(D)    cannot say anything

Answer 1

(B) greater than R×S

Reason: Every join operation is divided into two parts

First, cross product is calculated.

Second, then the given select conditions are checked. In case of natural join similar name attributes are checked thus increasing the computational cost of it.

CORRECT ME IF I AM WRONG.

Answer 2

Temp1 ∩ temp2 = Empty

Temp1 × Temp 2 = 3*3 = 9

Temp ⋈ temp2 = 3*3 [cross join operations] +9[checks to match two columns]

It should be greater than   R×S

Comments

Y wil u have cross join operations and checks to match the two columns seperate? They can be done together only right? compare each tuple of Temp1 with each tuple of Temp2, which will give 3*3=9. Why will we again check if there is any column matching in Temp1 and Temp2?

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Yes, correct.But since we have extra checks here the computation cost would be higher on natural join side.Isn't it?

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Y wil we have extra checks?

Answer 3

my question is this there is no common atrrib between R and S then why natural join operator do comparison and multiply operation.

explain pls!!!