Iterators
Access methods typically involve iterators, e.g.
Scan s = start_scan(Relation r, ...)
- commence a scan of relation
r
-
Scan may include condition to implement WHERE -clause
-
Scan holds data on progress through file (e.g. current page)
Tuple next_tuple(Scan s)
- return
Tuple immediately following last accessed one
- returns
NULL if no more Tuples left in the relation
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