Kevin Grittner wrote:
Grzegorz Jaœkiewicz<gryzman@xxxxxxxxx> wrote:
A failing of the SQL standard is that it uses the same mark (NULL) to show the absence of a value because it is unknown as for the case where it is known that no value exists (not applicable). Codd argued for a distinction there, but it hasn't come to pass, at least in the standard. If anyone could suggest a way to support standard syntax and semantics and add extensions to support this distinction, it might be another advance that would distinguish PostgreSQL from "less evolved" products. :-)
Theoretically, the distinction already exists. If you don't know a person's middle initial, then set it to null; if you know the person doesn't have one, set it to the empty string.
But from a practical point of view, that wouldn't go very far. Most *people* equate an empty string to mean the same as null. When I wrote my own data access layer years ago, I expressly checked for empty strings on input and changed them to null. I did this because empty strings had a nasty way of creeping into our databases; writing queries to produce predictable results got to be very messy.
-- Guy Rouillier -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
