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That's exactly what I look against on interviews. Slow SQL queries tend to work fine for some time, and as data grows, they start failing.

I'd want to hire a professional, who knows the perfect way of doing that, so for them it would be as easy to make it right, as to make it ugly.

Yes, in particular for data analysts using SQL to answer product/business questions in a one-off fashion

Unless the dataset grows, poorly optimised queries slow down superlinearly, and things start falling over.