Github user rmetzger commented on the pull request:
https://github.com/apache/incubator-flink/pull/275#issuecomment-67846346
I would suggest to use the Keys class also for Tuples.
If you have a Tuple3<Tuple2<String, Int>, Int, Int> and you select key 0
(which is a Tuple2), we internally handle this as keys[] = {0,1}.
If you really want to select only the String field of the Tuple2, you have
to use string -field section "f0.f0" and you'll get 0.
If you just use the "trivial" extraction (= directly using the user input),
you might cause unexpected behavior.
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