Need to be careful with that. There was a guy in California a few years back that decided the license plate "NULL" would be a fun joke, and he ended up being charged every ticket issued in the state where the license plate wasn't entered.
I recall pondering the mechanics of this back when I first read about it. Is some software actually replacing an input of "" (empty string) with "NULL"? Or is some comparison so loosely typed that a value of type null is considered equal enough to the string "NULL"?
'' when assigned to a char(1) becomes ' ' (char types are blank padded strings).
'' when assigned to a varchar2(1) becomes '' which is a zero length string and a zero length string is NULL in Oracle (it is no long '')
The conflation of empty string with a real null isn't great, but it doesn't also imply conflation of the string "NULL" which is what I'm trying to figure out. The four-character sequence shouldn't ever be considered something other than a four-character string, except for particular non-user-facing situations such as when actually writing code. Even spreadsheet software, which does all kinds of heuristics to find numbers in strings for example, doesn't treat the string "NULL" as anything other than a four-character string, to my knowledge.
