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We use a `queryGranularity`of `minute`during ingestion and query.

What a fascinating use-case!

Yes, that it is quite frustrating. Here is the link to the relevant documentation: https://druid.apache.org/docs/latest/querying/aggregations.html#:~:text=Do%20not%20use%20first%20and%20last%20aggregators%20for%20the%20double%2C%20float%2C%20and%20long%20types%20in%20an%20ingestion%20spec.%20They%20are%20only%20supported%20for%20queries.%20The%20string%2Dtyped%20aggregators%2C%20stringFirst%20and%20stringLast%2C%20are%20supported%20for%20both%20ingestion%20and%20querying. I tried looking at the source code but couldn't figure out the reason.

I use stringFirst and stringLast to get the first and last values of an event that has a fixed daily timestamp, effectively getting the latest and earliest values that were emitted that day. This works well, however you can't group by an aggregation so you can't

select count(*), latest(myfield) from table group by 2

because it is an agg of an agg. But I found you can actually group by it by using a scalar instead of

latest

, eg

json_value(parse_json(to_json_string("myfield")),'$.rhs', 'STRING'))

. Ideally you could just use

json_value

, but you can't seem to treat a

Complex<Tuple<T1,T2>>

as json even though it renders that way (probably an oversight in druid, no more than that).

Thank you all for your replies 😀. @David McHealy : Fortunately, we don’t have to group by that field, at least to my knowledge. Do you specify a timeColumn during ingestion, or are you using the default?

there is a PR to add this missing support - https://github.com/apache/druid/pull/10949 - posting here in case anyone in this thread wants to take that PR to the finish line 😉

@Abhishek Agarwal Thank you, that looks great 🙂 If I continue to be assigned on this project I might just pick that PR up. I have to brush up my java skills though 😅