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There is similar open-source project for Google Sheets: https://github.com/0x6b/libgsqlite (SQLite extension), which is a fork of https://github.com/x2bool/xlite (same idea but for Microsoft Excel spreadsheets)

Yes, it should.

Before you know what you can SELECT you should know FROM where does the data come.

Except maybe cases where there is no data source: SELECT 1; or SELECT NOW();

This project actually started as a fork of https://github.com/x2bool/xlite - SQLite extension for querying .xls and .xlsx spreadsheets.

How to use Rust to create loadable SQLite extensions

I too made a cross-platform GUI for Redis some time ago: https://github.com/rbmkio/radish

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