Empty Strings Aren’t Better Than NULLs
Prove me wrong.
Click through for commenters’ perspectives.
I’m not at the C.J. Date level of “NULLs are a mockery of the entire relational system and should be burned to the ground and that ground be salted and that salt be burned, just in case” but I do have my sympathies there.
An empty string has meaning: the value of a given attribute in this tuple is an empty string. NULL has no value and therefore violates first normal form (which, unlike my joking histrionics above, is an argument Date lays out in far too much detail for me to include here).
So what if you don’t know the value of a thing? Then the answer is, don’t store it! If there are certain attributes which may be missing at insertion time and are nonetheless relevant to maintain, use 6th Normal Form for each of those attributes. Then, the existence of a record indicates that it has a value and the lack of existence indicates that there is no value as of this time. This is quite different from NULL, about which we can only say “I don’t know if there is a value at this time, but if you’d like, I can do weird things with some of your queries if you happen to forget about this non-information.”