Doubt Database

Question

What is difference between attributes set of cross product and attributes set of joine ???

Comments

R(A,B) and S(B,C) are two relations then

RxS(A_RB_RB_SC_S) and R⋈S(ABC) 

For the Cartesian product to be defined, the two relations involved must have disjoint headers—that is, they must not have a common attribute name.

When we talk about cartesian product attribute B for both relations is considered different

It is usually required that R and S must have at least one common attribute, but if this constraint is omitted, and R and S have no common attributes, then the natural join becomes exactly the Cartesian product.

bu when we talk about Natural Join , Both B are same.

Answer 1

In case of Attribute set of Cross product, we get the complete cross product of two sets, whereas in case of join we get some sets of the attribute but with some special conditions .In case of join we get either whole cross product of two sets or less than cross product of two sets .