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

On Mon, 2010-12-13 at 17:15 +0000, Peter Geoghegan wrote:
> On 13 December 2010 16:08, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Mon, Dec 13, 2010 at 10:49 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> >> 2. pg_validate_foreign_key('constraint name');
> >> Returns immediately if FK is valid
> >> Returns SETOF rows that violate the constraint, or if no rows are
> >> returned it updates constraint to show it is now valid.
> >> Lock held: AccessShareLock
> >
> > I'm less sure about this part.  I think there should be a DDL
> > statement to validate the foreign key.  The "return the problem" rows
> > behavior could be done some other way, or just left to the user to
> > write their own query.
> 
> +1. I think that a DDL statement is more appropriate, because it makes
> the process sort of symmetrical.

OK, sold.

> Perhaps we could error on the first FK violation found, and give a
> "value 'foo' not present in table bar". It ought to not matter that
> there could be a lot of violations, because they will be exceptional
> if you're using the feature as intended - presumably, you're going to
> want to comb through the data to find out exactly what has gone wrong
> for each violation. On the off chance that it actually is a problem,
> the user can go ahead and write their own query, like Robert
> suggested.

I think a function would help here, so I'll do that also.

-- Simon Riggs           http://www.2ndQuadrant.com/books/PostgreSQL Development, 24x7 Support, Training and Services