[pravus]

> BTW the question I asked was about querying data without ever using a SQL language, like tapping directly into the data.

A lot of databases are just data structures written to disk in an efficient manner. There's nothing really stopping anyone from doing the same and implementing the query language as a direct API to these on-disk structures. In my mind this all just falls under the general category of random access files. This can be extremely performant if you are very knowledgeable of your use case and storage characteristics.

SQL on the other hand is a query layer on top of these data structure engines which gives you a more general purpose language to work with. It doesn't map directly to the underlying data structures so you can model data differently at a more abstract level. Ultimately it will be compiled down into some sort of routine that attempts to perform data access to those underlying data structures in as optimized a manner as it can figure out.

It's all about trade-offs. There are also plenty of storage engines that already give you an on-disk data structure in a box (e.g. RocksDB).