On 9/28/20 2:58 PM, Joe Abbate wrote:
Hello Tom,
On 28/9/20 17:25, Tom Lane wrote:
Domain-over-composite might be a slightly simpler answer than your first
one. It's only available in relatively late-model PG, and I'm not sure
about its performance relative to your other design, but it is an
alternative to think about.
"Domain-over-composite" meaning create a TYPE first (DATE, CHAR(1)) and
then a DOMAIN based on that type? (1) How late model are we talking?
The DOMAIN syntax doesn't seem changed from PG 11 to PG 13? (2) Can a
CHECK constraint specify attributes of the composite?
Note that attaching NOT NULL constraints at the domain level is almost
never a good idea, because then you find yourself with a semantically
impossible situation when, say, a column of that type is on the nullable
side of an outer join. We allow such constraints, but they will be
nominally violated in cases like that.
NULLs: Tony Hoare's "billion dollars of pain and damage" transported to
SQL.
Except that the case Tom is talking about would occur due to something like:
select table_a left join table_b on table_a.id = table_b.id where
table_b.id is null;
That has been very useful to me and I'm not sure that how anything you
replace NULL with to represent 'unknown' would change the situation.
Joe
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
