Re: Constraint documentation

The product name, when used in the documentation, is "PostgreSQL" with
appropriate html elements surrounding it.

Some parts that look or read oddly to me:
"you may expect troubles"
Use - if possible - (commas, not hypens, are customary here)
"does not currently" - drop "currently", it doesn't and we don't need to
predict the future (same goes for "are currently meant")
"therefore we recommend to avoid them" - they are unsupported, the implied
recommended is to not use them period, not avoid them if possible. Better
to say that it isn't enforced even though it is unsupported.

An alternative to consider as one the whole the reading of the v4 patch
just feels off and different than the rest of that section of the
documentation.

PostgreSQL does not support writing CHECK constraints that reference tables
(though it does not reliably prevent one from doing so). While normal
operations are likely to succeed even if you violate this rule it is
probable that a database restoration will fail. Use FOREIGN KEY
constraints or custom triggers for cross-table validations. For rows on
the same table you should use UNIQUE or EXCLUDE constraints when
applicable, or a custom trigger otherwise.

David J.

On Tue, Oct 30, 2018 at 8:50 AM Patrick Francelle <patrick(at)francelle(dot)name>
wrote:

> On 08/10/18 07:02, Pantelis Theodosiou wrote:
> >
> > I like this:
> >
> >> "Postgres does not currently support CHECK constraints containing
> > queries, therefore we recommend to avoid them."
> >
> > Perhaps adding:
> >
> >> CHECK constraints are currently meant to be used as *row constraints*
> > only.
> >> Use - if possible - UNIQUE or EXCLUDE constraints. for constraints
> > that involve many or all rows of a table,
> >> and FOREIGN KEY constraints for cross table constraints.
> >> More complex constraints will be available when ASSERTION are
> implemented.
> >
> > And then adding some warning about using functions in CHECK constraints
> > to bypass current limitations.
> >
> > Pantelis Theodsoiou
>
> Hi,
>
> I have rewritten the patch to include your remarks.
> In fact, the whole patch is now based on it, so thank you.
>
>
> Patrick Francelle
>