On Wed, Aug 12, 2009 at 10:51:04AM +0200, Willy-Bas Loos wrote: > > SELECT r IS NULL, r IS NOT NULL > > FROM (VALUES (1,NULL)) r(a,b); > > > > returns FALSE for *both* columns. How can a row be both NULL *and* > > non-NULL? > > Actually, the value is neither NULL, nor non-NULL. > Part of it is NULL and part of it isn't so neither "IS NULL" is true, > nor is "IS NOT NULL"
Nope, I still don't get it. Why treat rows specially? If this was true, then what should: SELECT a IS NULL, a IS NOT NULL FROM (SELECT ARRAY [1,NULL]) x(a); evaluate to? As "part of it" is NULL and part isn't then, by your reasoning, it should return TRUE for both. PG doesn't and I think this is much more useful behavior. The value itself is not unknown, it just happens to contain some unknown values. Having a row that consists entirely of NULL values being treated as NULL is OK, but some weird halfway house is horrible. Standards' conforming, but still horrible. -- Sam http://samason.me.uk/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
