I know how to remove files in order to make them impossible to recover. But, how do I remove rows from a MySQL table in a POSIX environment in a way that leads to the same results? I'm currently rewriting all data with a nullified string with the same length as the original data before I proceed with deleting the row. Does it work? If not, how do I make it work?
I doubt you will be able to do this in such a way that you can say with confidence that the original data is completely gone.
Take a look at this analysis which includes a case study of MySQL retention;