Great!
Note that the infrastructure for %PARALLEL is substantially improved in the upcoming 2016.2 release. If your query can be parallelized, you ought to see even better performance there.
You want to use the concatenate operator: ||
e.g.:
SELECT EventType || ';' || InitiatedAt as k, COUNT(*) as cnt FROM HS_IHE_ATNA_Repository.Aggregation WHERE EventType = 'LOGIN' AND LocalDateTime > '2016-02-16 11:00:00' GROUP BY EventType, InitiatedAt
+ is the addition operator, which implicitly treats string values as 0.
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You have the right idea to 'literalize' the 0 so it isn't treated as a parameter, but the syntax isn't quite right. Try:
Then the optimizer should know that this condition will be non-selective.