Re: ALTER TABLE ... ADD FOREIGN KEY ... NOT ENFORCED

Simon Riggs <simon@2ndQuadrant.com> writes:
> On Sun, 2010-12-12 at 17:57 -0500, Tom Lane wrote:
>> Huh?  It allows you to postpone the check until commit.  That's far from
>> not enforcing it.

> This clearly implies that un-enforced constraints are not checked at
> commit.

[ shrug... ]  I can't argue with you about what may or may not be in an
unpublished draft of an unratified version of the standard, since I
don't have a copy.  But allow me to harbor doubts that they really
intend to allow someone to force a constraint to be considered valid
without any verification.  This proposal strikes me as something mysql
would do, not the standards committee.  (In particular, can a constraint
go from not-enforced to enforced state without getting checked at that
time?)

Even if you're reading the draft correctly, and the wording makes it
into a released standard, the implementation you propose would break our
code.  The incremental FK checks are designed on the assumption that the
constraint condition held before; they aren't likely to behave very
sanely if the data is bad.  I'd want to see a whole lot more analysis of
the resulting behavior before even considering an idea like this.
        regards, tom lane