Compare SQL Datetime if Empty or NULL

I have two TEXT fields in my database table named, start_time and expires_time. I store these times in the format of YYYY-MM-DDTHH:MM:SS.SSSZ (UTC, GMT).

I would like to be able to query these fields based on the current local time to find out if a record’s time is about to start, has already started, or has expired. I need to do this all in the SQLite code.

There are cases where a record can be created with no start_time or expires_time. Should I change the field format to be of DATETIME for this situation and use NULL? Or will SQLite do the date compare if the fields are of TEXT and the field is empty ("")?

Many Thanks!

As long as the text field truly contains an empty string, as opposed to being null, it should work fine.