Greetings,
We're currently evaluating MonetDB for a analytical DW and so far we are happy with the results.
I am trying to implement a grouping function that calculates a a value over a set of strings, so that my queries would read like this:
select metric, *udf_aggregate*(string_column) from table group by metric;
for a bit of background, we're using a dinstinct value sketch called HyperLogLog http://metamarkets.com/2012/fast-cheap-and-98-right-cardinality-estimation-f... http://blog.aggregateknowledge.com/2012/10/25/sketch-of-the-day-hyperloglog-...
and we're currently storing estimations for each time period (day). HLL lets you merge/aggregate a set of estimations (each estimation is a vector of numbers, we're currently storing it as a string) for an arbitrary range, and still have an accurate estimation. (I'm sure the literature doesn't call it estimations, sorry for my English)
what I would like is a custom UDF like the one provided in MonetDB src (*reverse*)**but that would operate and behave like an aggregate function.
Right now, I'm not considering using it for types other than /string/ (no need for polymorphic right now). Is this possible with an UDF? I found a way of registering aggregate functions on the mailing list, but the HLL is complex enough to warrant its own C impl, instead of a MAL function.
Thanks, Miguel
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