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

On 2014-06-14 16:44:10 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)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?

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.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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