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You can do some kinds of joins in druid. Since you say user info can be updated, you might look at lookup tables. (There's a link in the joins page linked above.)

Thanks Ben ! Will look into this.

I believe you can group by a value fetched from a lookup, if that's what you mean. I just realized, I should have mentioned the limitation that looks can only be key:value, ie, one key, one value per row. If you need more than that, there can be other options. (For the second, I'm not sure what you mean about topN on the lookup response.) Lookups do have various limitations you should check in to. btw, there's work being done on broadening join functionality and support.

@Ben Krug Yeah, I meant I have one key and multiple values in the lookup. I would like to do groupby on any of them. What other options do I have here ?

You can group by the key or value, shouldn't be a problem. Imo, if lookups work, that's probably the best option by far right now, mainly since you want to have updates to the table (and also it doesn't need timestamps).