James B. Byrne wrote: > The basic issue is episodic duration, expressed as columns named > dt_effective_from and dt_superseded_after. Both are datetime types > containing values normalized to utc. You see where this is going. > > The issue is what to enter when the value is known to be unknown, as If it's unknown use null. > in some indeterminate future date, which may be never. That's not unknown that's "in the future". > I read that > relational set values should never be null, as null is indeterminate > for WHERE clauses and may result in unexpected results. Only if you use it to mean something other than unknown. If you have an event that starts '2001-01-01 01:01:01+01' and ends "null" then you can confidently say "don't know" as to how long that event is. > On the > other hand, setting some artificially excessive future date seems in > its place seems, to me, to have its own problems. Which is where you reach for the handy datetime literals as described below: select 'infinity'::timestamp without time zone; select '-infinity'::timestamp without time zone; -- Richard Huxton Archonet Ltd -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
