Re: UPDATE SET (a,b,c) = (SELECT ...) versus rules

On 2014-06-14 19:27:03 -0500, Jim Nasby wrote:
> On 6/14/14, 3:51 PM, Andres Freund wrote:
> >>Hm.  But you might as well use a trigger, no?  Is anyone likely to
> >>>actually be doing such a thing?
> >I don't think anybody is likely to do such a thing on an actual table,
> >but INSTEAD OF for views is pretty new. For a long time rules were the
> >the only way to implement updatable views (including any form of row
> >level security).
> >
> >>>It's conceivable that we could optimize the special case of NEW.*,
> >>>especially if it appears in the rule query's targetlist.  But it's
> >>>trouble I don't really care to undertake ...
> >I think it's fine to just throw an error.
> 
> If there was a showstopper to moving forward with rule support I think
> it'd be OK to throw our hands in the air, but that's not the case
> here.
> 
> I'm in favor of doing the substitution, just like we do today with
> RULES, warts and all. We already warn people against using rules and
> that they're very difficult to get correct, so I don't think double
> eval of an expression should surprise anyone.

It makes a formerly correct/safe rule unsafe. That's a showstopper from
my POV.

There's *STILL* no proper warning against rules in the manual, btw.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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