I came from a MSSQL background and eventually worked on an MySQL project with somebody who had a TON of MySQL experience by way of symfony.

I was explaining that not all of his non-aggregated columns were in his group by, so his query wasn't going to work.... but what do you know, MySQL will just return whatever it feels like from the group in that situation. I expected it not to run at all.

I think there are some flags etc you can use to enable to stricter behavior but it was one of the wildest footguns I've ever seen.