Aggregation across multiple DRUID datasource

Hello Druid Users,
I understand join is not an priority as of now [1], does anyone have a similar use case needing to join/union across multiple data sources? And if so, how do you tackle the problem? Thanks!

Thanks,
Guang

[1] http://druid.io/docs/latest/querying/joins.html

There are two features Druid has that are in this area.

One is union datasources, that lets you query multiple datasources as if they were a single one: http://druid.io/docs/latest/querying/datasource.html#union-data-source

Another is query time lookups, that lets you join small (broadcast in memory) “lookup” tables onto regular datasources: http://druid.io/docs/latest/querying/lookups.html