Compare the Nested-loop join and block-nested loop join

Ans: Nested  loop join - It is costly as worst case cost, no. of block accesses needed is n_r * b_s + b_r  where b_s and b_r denote no. of blocks containing  n_s and n_r tuples of relations S and R, relevant and in best case there will be b_r + b_s block accesses

Block-nested-loop join - In worst case no. of block accesses is b_r*b_s + br. In best case, b_r +b_s block accesses will be needed.