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.
"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."