An idea I was recently thinking about would be to prepare an (SQLite?) DB with all the data the customer is allowed to access (whether their own data, or propri

An idea I was recently thinking about would be to prepare an (SQLite?) DB with all the data the customer is allowed to access (whether their own data, or proprietary data they're licensed to access and extract) and then let them run raw queries. The advantage of using SQLite (as opposed to your primary DB) is that you don't have to care about sanitizing the queries or ensuring they don't see what they're not meant to because the user-specific DB only ever has data they are allowed to access, so even allowing them to run raw queries against (or download the whole database file) would be fine.