Pass 1:We enumerate the strategies for each base relation using a linear search and all
available indexes on the relation. These partial (single-relation) strategies are partitioned
into equivalence classes based on any interesting orders, as discussed above. An additional
equivalence class is created for the partial strategies with no interesting order. For each
equivalence class, the strategy with the lowest cost is retained for consideration in the next
pass. If the lowest-cost strategy for the equivalence class with no interesting order is not
lower than all the other strategies it is not retained. For a given relation R, any selections
involving only attributes of R are processed on-the-fly