Hey, As a matter of fact, you do not need a Flink's CEP library to run the same query. The same functionality can be achieved by simple tumbling window with a “median” aggregate (“median" you would have to implement by your self).
https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/operators/windows.html Piotrek > On 23 Nov 2018, at 16:32, Piotr Nowojski <pi...@data-artisans.com> wrote: > > Hi, > > Yes, sure. Just use CEP on top of KeyedStream. Take a look at `keyBy`: > > https://ci.apache.org/projects/flink/flink-docs-release-1.6/dev/stream/operators/ > > <https://ci.apache.org/projects/flink/flink-docs-release-1.6/dev/stream/operators/> > > Piotrek > >> On 23 Nov 2018, at 16:04, Spico Florin <spicoflo...@gmail.com >> <mailto:spicoflo...@gmail.com>> wrote: >> >> Hello! >> >> I'm using Flink 1.4.2 and I would like to use a group by operator based on >> value of my event stream. The functionality that I would like to achieve is >> similar to the following Esper EPL >> (excerpt >> http://esper.espertech.com/release-5.2.0/esper-reference/html/epl_clauses.html#epl-grouping-aggregating >> >> <http://esper.espertech.com/release-5.2.0/esper-reference/html/epl_clauses.html#epl-grouping-aggregating>) >> >> >> select symbol, tickDataFeed, median(volume) >> from StockTickEvent.win <http://stocktickevent.win/>:time(30 sec) >> group by symbol, tickDataFeed >> <> >> >> So, does the Flick CEP support such a group by functionality? >> >> If yes what is syntax? >> >> >> >> I look forward for your answers. >> >> >> >> Best regards, >> >> Florin >> >> >> >> >> >> (excerpt >> http://esper.espertech.com/release-5.2.0/esper-reference/html/epl_clauses.html#epl-grouping-aggregating >> >> <http://esper.espertech.com/release-5.2.0/esper-reference/html/epl_clauses.html#epl-grouping-aggregating>) >> "You can list more then one expression in the group by clause to nest >> groups. Once the sets are established with group by the aggregation >> functions are applied. This statement posts the median volume for all stock >> tick events in the last 30 seconds per symbol and tick data feed. Esper >> posts one event for each group to statement listeners: >> In the statement above the event properties in the select list (symbol, >> tickDataFeed) are also listed in the group by clause. The statement thus >> follows the SQL standard which prescribes that non-aggregated event >> properties in the select list must match the group by columns." >> >
