Selection is implemented in Minibase by calling the function Eval at the end of an iterator. This function takes a list of conditions and applies them. For selection on a single relation, the iterator is a file scan iterator or an index scan iterator (if some selection condition matches an index --- the optimizer will `push' selections whenever a suitable index is available). If the selection follows a join, the iterator is a join iterator.
The public interface for the Eval function is available here.
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