Assume events of either type A, B, C or D are being emitted. I want to detect whenever an event of type A is followed by an event of type B. In other words, I want to detect a sequences, for which Esper's EPL provides the -> operator.
However, what I described above is ambiguous, what I want is the following: Whenever a B is detected, I want it to be matched with the most recent A.
I have been playing around with EPL's syntax, but the best I could come up with was that:
select * from pattern [(every a=A) -> b=B]
This, however, matches each B with the oldest A that occured after the last match. Weird...
Help is much appreciated! :P
I use joins a lot for the simple matching. The other option is match-recognize. The join like this.
select * from B unidirectional, A.std:lastevent()