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\textit{Greedy Operator Order(GOO)}  GOO maintains a set of join trees, each of which initially consists of one base relation. The algorithm then combines the pair of join trees with the lowest cost to a single join tree.This approach is capable of building join orders fast enough. Advantage of this approach is due to the evaluation of intermediate results. [L. Fegaras. A new heuristic for optimizing large queries. In  DEXA, pages 726–735, 1998.] [\cite{GOO Heuristc}]  have shown the superiority of this approach compared with others others.