Logical window = Time-based window; Physical window = Tuple-based windows
SELECT itemID, avg(Offer)
OVER(ROWS 39 PRECEDING ORDER BY TIME)
WHERE ItemID = 0021
When BIDS is instead a data stream, the “ORDER BY TIME” clause becomes redundant, and clauses such as “FOLLOWING” are often not supported in continuous query languages. However, these languages still provide a “PARTITION BY” clause (or the more traditional “GROUP BY” clause), whereby a user can specify that the average of the last 40 offers must be computed for all items, not just item 0021. In addition to entailing powerful and flexible analytical queries on ordered sequences and time series, as in databases, windows on data streams play the key role of synopsesand...
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