|From:||David Fetter <david(at)fetter(dot)org>|
|To:||David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>|
|Cc:||Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: [PATCH] Equivalence Class Filters|
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On Sun, Dec 20, 2015 at 10:27:35PM +1300, David Rowley wrote:
> On 16 December 2015 at 13:26, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > There is an interesting real world case where we might get some
> > use of these thoughts.
> > If we have Orders and OrderItems (FK->Orders) and we also know
> > (and can Assert) Order.order_date <= OrderItems.ship_date then a
> > restriction on Orders.order_date > X => OrderItem.ship_date > X
> > when the two tables are joined on OrderId and also a restriction
> > on OrderItems.ship_date >= X => Orders.order_date < X when the two
> > tables are joined on OrderId
> > Such an assertion could be checked during the FK check, so would
> > not be expensive to maintain.
> > One for the future, at least, since we don't have any way of
> > expressing or enforcing that just yet.
> That does sound interesting, but it's important to remember that
> referenced tables are not updated in real time in that same way that
> indexes are.
Is getting them so even remotely possible, given the system we have
David Fetter <david(at)fetter(dot)org> http://fetter.org/
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