Hi everyone, i work with 3 database in Metabase and i already upvote the request for questions with more than one database in Git (https://github.com/metabase/metabase/issues/3953) 
Because it’s a big request, anyone have any solution to mount a data warehouse and connect to Metabase?
You could use any of the supported databases as a data warehouse, so not sure what you're looking for.
If you want to use multiple databases without going to the trouble of a DW, read this:
@yuriandreoli BigQuery? I think the closest that exists is Dremio, but there’s currently no functional driver
I’m also interested in any thoughts on this matter, I would like to create a data warehouse and connect it to Metabase, in which I need to “join” a database in mysql with a database in mongo db. However, I’m really confused on how to approach it (I’m a newbie in metabase), do I need to create a data warehouse in BigQuery, for example? and then, how often do i need to update my data warehouse? Are there others technical requirements? Is there a documentation on this subject? Thank you.
@Larissa A data warehouse has nothing to do with Metabase specifically. It’s just a single place where all your databases are accessible from, so you can create queries that join between tables.
We have a slightly outdated blog post, which will get an update very soon: https://www.metabase.com/blog/which-data-warehouse-to-use/index.html
Then when you add that data warehouse to Metabase as a data source, then Metabase can also join between your databases in the data warehouse.