Support for lookup into a multi-value dimension

[sandeep217]

Hi,
Lookups currently support a 1x1 and Nx1 mapping. Often there's a need to do a lookup against 1xN mapping. A common example is a lookup that maps userid to user-groups where a user may belong to more than one user groups. Denormalizing at ETL may not be desirable if user to user-group mapping changes over time.

[drcrallen]

Just FYI, this is not easy in the current way lookups are handled. I'm not sure if @b-slim has considered this case for #2291 and other LookupExtractor stuff

[b-slim]

@sandeep217 i am currently working on this, will send a proposal soon!

[kyrozetera]

We are evaluating Druid for our use-case and this is the one thing I believe we are lacking. @sandeep217 's example is very similar to our case since our mapping changes fairly regularly, so I would like to 👍 this feature.

[sandeep217]

@b-slim do you have the proposal ready? sirpkt's proposal looks like is for a different feature.

[yurmix]

#7009

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