My Dad ran an online storefront. He needed a few thousand products reclassified as in-stock instead of unavailable. It's easy to change them one at a time in the storefront's backend, but they offered no way to change more than one at a time.

Turns out the storefront had a MySQL interface where you could just type queries into it and run them all you wanted, but he was always too scared of causing big problems and never used it. Writing MSSQL queries is a huge part of my job. They're almost exactly the same language.

It would have taken him weeks to do it all by hand. I got it done in two minutes, and most of that was analyzing their database schema.