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I have two doubts:

1) A natural join B

What will be the result when B don't have any tuple in it. Like in B their is relational algebra expression which is selecting Cars of green color but their is no green color car in table. What will be the result in this case.

2) A / B

In above divison if B is a relational algebra expression returning nothing ( like the B in case 1). What will be the result ?

A natural join B = Phi i.e. nothing since Natural join = Condition on same attribute(cross product which gives 0)

A/B when B=0 then output is A only.

ok thanks. Where you learned this ?

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