HiveSQL is a SQL Server instance
that is kept up to date with the blockchain data so it's easy to query. 
@arcange runs the one I use and I'm not sure if there are others. There is also HAF that in don't fully understand, but it may also allow queries. I have also used a library for direct blockchain access, but that was slower.
I needed the MS library for the Python queries to work. They provide it for Linux.
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