Re: Help with restoring a dump in Tar format? (dependencies/ordering)

On 6/5/2017 5:32 PM, David G. Johnston wrote:
> On Mon, Jun 5, 2017 at 5:15 PM, Ken Tanzer <ken(dot)tanzer(at)gmail(dot)com
> <mailto:ken(dot)tanzer(at)gmail(dot)com>>wrote:
>
> From the docs:
> https://www.postgresql.org/docs/9.6/static/sql-createtable.html
> <https://www.postgresql.org/docs/9.6/static/sql-createtable.html>
> "Currently, CHECK expressions cannot contain subqueries nor
> refer to variables other than columns of the current row. The
> system column tableoid may be referenced, but not any other
> system column.
>
>
> I wonder if that should say "should not," or be followed by
> something like this:
>
>
> Make it say "must not" and I'd agree to change the word "cannot" and
> leave the rest. Adding a note regarding functions seems appropriate.
>
> Aside from being a bit more verbose there is nothing useful that
> writing this as "CHECK function()" provides that you don't also get by
> writing "CREATE TRIGGER". In a green field we'd probably lock down
> CHECK a bit more but there is too much code that is technically wrong
> but correctly functioning that we don't want to break. IOW, we cannot
> mandate that the supplied function be immutable even though we
> should. And we don't even enforce immutable execution if a function
> is defined that way.

indeed, any sort of constraint that invokes a function call which looks
at other tables could later be invalidated if those other tables change,
and postgres would be none the smarter. the same goes for trigger
based checks.

--
john r pierce, recycling bits in santa cruz