defines abstract semantic for continous queries
CQL := SQL + operators that map between relation and stream (e.g. windows)
Select P.price
From Items[Rows 5] as I,
PriceTable as P
Where I.itemID = P.itemID
Items
is a stream,PriceTable
is a stored relation, and[Rows 5]
specifies a 5-element sliding window.Even this simple query has no single obvious interpretation that we know of. For example, is the result of the query a stream or a relation? What happens to the query result when the price of a recently purchased item – i.e., an item still within the 5-element window – changes?
C.f. Apache Calcite's Streaming Extension, SamzaSQL and Kafka's KSQL / ksqlDB.