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Re: [flink-cep] Flick CEP support for the group By operator


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).


Piotrek

On 23 Nov 2018, at 16:32, Piotr Nowojski <piotr@xxxxxxxxxxxxxxxxx> wrote:

Hi,

Yes, sure. Just use CEP on top of KeyedStream. Take a look at `keyBy`:


Piotrek 

On 23 Nov 2018, at 16:04, Spico Florin <spicoflorin@xxxxxxxxx> 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


select symbol, tickDataFeed, median(volume) 
from 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 



"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."