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

Andres Freund <andres@2ndquadrant.com> writes:
> On 2014-06-14 15:48:52 -0400, Tom Lane wrote:
>> Well, it wouldn't be "unsafe" (barring volatile functions in the UPDATE,
>> which are unsafe already).  It might be slow, but that's probably better
>> than failing.

> I forgot the details, but IIRC it's possible to write a ON UPDATE ...
> DO INSTEAD rule that's safe wrt multiple evaluations today by calling a
> function passing in the old pkey and NEW. At least I believed so at some
> point in the past :P

Hm.  But you might as well use a trigger, no?  Is anyone likely to
actually be doing such a thing?

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 ...
        regards, tom lane