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Custom Trigger + SQL Pattern


I have a use case in which im grouping a stream by session id - so far
pretty standard, note that i need to do it through SQL and not by the table
In my use case i have 2 trigger conditions though - while one is time
(session inactivity) the other is based on a specific event marked as a
"last" event.
AFAIK SQL does not support custom triggers - so what i end up doing is doing
group by in the SQL - then converting the result to a stream along with a
boolean field that marks whether at least one of the events was the end
event - then adding my custom trigger on top of it. 
It looks something like this:

 Table result = tableEnv.sqlQuery("select atLeastOneTrue(lastEvent),
sessionId, count(*) FROM source Group By sessionId");
tableEnv.toRetractStream(result, Row.class, streamQueryConfig)
                .filter(tuple -> tuple.f0)
                .trigger(new SessionEndedByTimeOrEndTrigger())
                .process(...take last element from the group by result..)

This seems like a weird work around to, isn't it? my window is basically of
the SQL result rather than on the source stream. Ideally i would keyby the
sessionId before running the SQL but then a) would I need to register a
table per key? b) would i be able to use the custom trigger per window?

basically i want to group by session id and have a window for every session
that supports both time and custom trigger. Assuming i need to use SQL
(reason is the query is dynamically loaded), is there a better solution for

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