On Thu, Apr 28, 2005 at 02:04:29PM +0200, Marco Colombo <pgsql@xxxxxxxxxx> wrote a message of 146 lines which said: > No. NULL is NOT 'None', nor 'undef', and definitely not NULL as in > C. Thanks for the very good and detailed explanation of NULL in SQL. Curious people may note that the strange semantics of NULL are heavily criticized in C. J. Date and Hugh Darwen "A Guide to the SQL Standard" (Addison-Wesley) [Side note: I was perfectly aware for NULL in C, where it is just an ordinary zero, that's why I only mentioned Perl and Python.] > marco=# select 2 = NULL; > ?column? > ---------- > > (1 row) Even better, you can write; registry=> select NULL = NULL; ?column? ---------- (1 row) > Depending on what you're trying to achieve, you may need to split > the table (normalization the theorists call it). Yes, I noticed in similar organizations that the Hosts table was split in one table for names and one for addresses, may be for exactly that reason. > Review your design, maybe either the table schema or the choice of > the primary key is not natural for your database. At the present time, it seems that, practically speaking, the technique proposed by Sebastian Böck (two index) is perfectly fine. This technique can be summarized as "PostgreSQL, I tell you to treat all NULL addresses as being the same value". ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster
