Given a table definition like:
create table foo (i integer check (i > 0));
I noticed the following works in Oracle but fails in Postgres:
insert into foo values(null);
I was curious about what the standard might say, and had been
meaning to buy Date's book for some time, so broke down and
did so.
According to Date, a check contraint should fail if the expression
evaluates to false. It appears that Postgres only passes the
check constraint if it evaluates to true. In three-valued logic,
these statements aren't equivalent. He has a paragraph about
nulls and check contraints in chapter 14, I believe, and his
explanation makes it clear that Oracle is right, Postgres wrong.
It's easy to fix by adding a check for null to the constraint,
and afterwards the SQL still works with Oracle, but it's still
a bug...
- Don Baccus, Portland OR <dhogaza@pacifier.com> Nature photos, on-line guides, Pacific Northwest Rare Bird Alert
Serviceand other goodies at http://donb.photo.net.
