In your documentation I see this:
However, it is very unclear what these properties represent. Can you please explain what fieldNames, fnAggregate, fnCombine, and fnReset are with a simple example.
My use case is that I have an input row with metrics A and B.
I would like to define a metric C where C = A*B so that after ingestion I can use C in aggregations. What’s the best way to accomplish this…
Also, I have a few questions on querying in general:
Is it possible to filter based on metrics or can you only filter based on dimensions? For instance if I had a metric Amount and I wanted to filter out the rows where Amount < 500, what would be the best way to approach this? Would I have to make Amount a dimension and then write a JS filter to parse the string to an integer and check if that integer is less than 500?
Another question - how could I groupby days of the week. If I wanted metrics for Sunday, Monday, …? Is this possible?
Finally, is there a way to query Druid for datasource metadata. In other words, can you get from Druid all of the ingested datasources as well as their specs (dimensions and metrics)?
Sorry that these questions are all over the place.