Some of the stuff I've struggled with the most over the years have been SQL constraints that are not documented. I remember (probably like 10 years ago), I depl

Some of the stuff I've struggled with the most over the years have been SQL constraints that are not documented. I remember (probably like 10 years ago), I deployed an update to an ancient Windows Forms implementation that deprecated some login and instead made use of Windows Authentication. It worked like a charm for all users, but one! Checked everything, replicated the machine, tried so many weird stuff, and in the end, what was happening is that the "Users" table had a constraint in the number of characters for the username. This username was over the limit and was not being validated... Another one was a report that was giving the wrong amount, but getting the data from database seemed to do the math right... it was the damn Money datatype, changed to decimal, done...