Hey @alessyl! Thanks for reaching out.
I had to do some testing because I haven't worked with the Google Sheets resource before, but it seems to return an object in the form of { index: { column_a: 'value_a', column_b: 'value_b' } }. This means that it's already well-formatted for querying with SQL.
The below configuration works for me:
Let me know if this setup is useful to your particular use case! I'm happy to answer any follow-up questions you might have, as well.