Suppose we have 2 tables R1(ABCD), R2(DE) . R1 has 500 entries whereas R2 has 1500 entries. Here D is a candidate key. If we join them using natural join. How many entires would be there in the resultant table and why ?

500....we have 1500 entries in r2 which are distinct as d is primary key...now for maximum if every d entry of r1 is distinct we will have 500 entries if not we will have less than 500 entries...so maximum 500 entries possible