Subtable query under the hood

I am working on optimizing the backend of my project and exploring the optimization of database queries. In the course of numerous tests and comparisons, it turned out that the most productive solution is the standard Wappler queries with subtables. This outstripped even MongoDB queries in speed, where documents with the entire complex structure were stored in the database. It is also faster than custom queries with aggregation to obtain a complex structure of documents. And so, in order to completely close the optimization needs, I lack some features when using sub-table queries in the Wappler:

1. Important! The ability to query sub-tables on several levels. If there are more sub-tables in the sub-table, when we request, we will receive data only of the 1st level of the sub-table. Data acquisition from all levels is required.
2. There is not enough opportunity to select certain fields when selecting a subtable.
3. There is not enough possibility to attach data from another table when selecting a subtable.

@patrick please tell me exactly what a sub-table query looks like in the code? Is this a separate request? Is the data merging happening outside the database?

These questions would help me recreate a complex query with my settings and get the maximum possible speed of receiving data from the server.