Hello,
On 2018-05-17 10:40, Dominique Devienne wrote:
On Wed, May 16, 2018 at 8:33 PM Keith Medcalf <kmedc...@dessus.com> wrote:
SELECT coalsce((select action
from blocked
where mail='...'), 'OK') as action;
Nice one Keith. Works (see below), but I find it a bit intuitive,
since returning no row is somehow not intuitively equivalent (in my mind at
least)
to a scalar row with a NULL value. Your query makes no distinction between
these two cases.
Quite justly -- let us not introduce multi levels of non--existence (a
source of many bugs):
(1) semi non--existence / a value ``NULL'' / a person saying ``Hello, I
do not exist'';
(2) virtual non--existence / a value ``UNDEFINED'' / a person not
existing virtually, because it is silenced (though breathing);
(3) literal non--existence / a value not existing literally / a person
not existing literally;
A NULL column (blocking) ``action'' in a table ``blocked'' is an error
and should be avoided -- it means ``you are blocked, but I do not know
how''. If someone wants a (lately bound) default action, let the name be
``DEFAULT'' -- not NULL.
-- best regards
Cezary H. Noweta
P.S. I know it is hard to return to a life after a programming in some
very flexible lang, in which every even simplest task can be done in a
trillion ways :)
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