Re: Minor correction in alter_table.sgml

* Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> >> I had considered removing those but thought that some users might think
> >> that they're only "altering" one table and therefore felt it made sense
> >> to keep those explicitly listed.
>
> > I agree with Stephen; it's not crystal clear from the user's POV that
> > the command is altering two tables. It's worth mentioning this
> > explicitly; otherwise this is just a documented gotcha.
>
> Well, it already is shown explicitly in the syntax summary. The text
> is simply trying to restate that in an easily remembered fashion, and
> the more exceptions, the harder it is to remember. You might as well
> forget trying to provide a rule at all and just say something like
> "Most forms of ALTER TABLE can be combined, except as shown in the
> syntax diagram."

I do wonder if perhaps we should change 'action' to something like
'combinable_action' or something more explicit which we could easily
refer to later in a statement along the lines of:

Multiple combinable_actions specified in a single ALTER TABLE
statement will be applied together in a single pass over the table.

> (Of course, maybe the question we ought to be asking here is why
> ATTACH/DETACH PARTITION failed to go with the flow and be a
> combinable action.)

I did wonder that myself but havne't looked at the code. I'm guessing
there's a reason it's that way.

Thanks!

Stephen