Comment by flukus

At least that was an accidental conversion and an understandable mistake, I've seen the same with dates stored as strings from devs unaware that dates are just integers with a lot of maths to make them meaningful.

At once place our end of month billing was getting slower and slower over the course of months, from one hour out to about twelve and it had to baby sit and run in batches in order to not bring the whole database to it's knees. We couldn't change the mess of legacy classic asp of course, but adding a couple of actual date columns calculated from the string fields on insert/update bought the whole process down to seconds.