Storing 'invalid' date in a database

Question

I am storing some records in a database. A record has a 'last visited' field which is a timestamp. If a record has not been visited yet, the timestamp is invalid. I am currently storing a future date e.g. '2101-01-01 00:00:00' in the 'last visited' field, to denote an invalid date.

Is there a better way to indicate an 'invalid' date. What is the recommended 'best practise' for doing this?

I am using MySQL, but ideally, the recommendation should be db agnostic

Answer 1

Store a NULL value instead. MySQL timestamps are pretty screwed up, so you might need to change your table schema to encourage it to let you put a NULL in there; I use DATETIME instead, it's a little less weird than TIMESTAMPs in MySQL.

Answer 2

The appropriate method of storing something of no value is to simply provide no value. That is to say, a null. Storing anything else and treating it as a magical value is often problematic. There are times when the magical value can be a valid value, and now you have no method of distinguishing the two.

Answer 3

I would just leave the field null.

If they've never visited the record, it shouldn't have a timestamp at all.