Indeed, we had to recently work with 500k patients' appointments. Database table Appointment had a date and "actually met" flag - sounds simple enough, right? N

Indeed, we had to recently work with 500k patients' appointments. Database table Appointment had a date and "actually met" flag - sounds simple enough, right? Nope - doctors were "meeting" dead people, different departments had different rules about whether phone calls were included and what did the "actually met" flag actually mean.