Re: explain plan difference

Thanks very much for the explanation Tom !! You are correct - there are
dropped columns in the original.

Cheers,

Steve

On Mon, Nov 4, 2019 at 3:01 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Steve Baldwin <steve(dot)baldwin(at)gmail(dot)com> writes:
> > I guess the difference doesn't have a huge bearing (as far as I can tell)
> > on the result, but it just seems odd that the inner-most 'Output' step
> > outputs the entire row in the case of the copy and only the required
> field
> > in the case of the original table. What triggers that behaviour?
>
> The plan with the full output row is actually slightly cheaper, or at
> least so the planner thinks, because it saves a projection step.
> I imagine the reason you're not getting that with the original table
> is that there are some dropped column(s) in the original table, forcing
> the projection to be done to get rid of them.
>
> regards, tom lane
>