NOOB Q! How to transform data across relationships

This is the first step you take in BI, it's called ETL. We have to filter the trash

In your case it is done with nested queries in SQL. Imagine that I have a catalog of clients, historic, but prepare a study on the last year my main clients. The main customers based on what? If your answer is billing, then you should filter my customer catalog, based on multi-year invoices.

This query will give a single-column subtable with all customers (only their id) to the one that was billed last year and will be the filter for the Customers table

(SELECT DISTINCT IdCliente FROM TablaFactura WHERE (FechaFactura >= 01/01/2019 AND FechaFactura <= 31/12/2019))

Query to load customers.

SELECT (the fields you're interested in in the comma-separated customers table)

FROM TablaClientes

WHERE (SELECT DISTINCT IdCliente FROM TablaFactura WHERE (FechaFactura >= 01/01/2019 AND FechaFactura <= 31/12/2019))

I hope it helps.