Re: checking my understanding of TupleDesc

Hi,

On 2019-11-12 17:39:20 -0500, Tom Lane wrote:
> > and under what other
> > circumstances one would only encounter 'cleaned up' TupleDescs with
> > no dropped attributes, and contiguous numbers for the real ones?
>
> I don't believe we ever include dropped columns in a projection result,
> so generally speaking, the output of a query plan node wouldn't have them.
>
> There's a semi-exception, which is that the planner might decide that we
> can skip a projection step for the output of a table scan node, in which
> case dropped columns would be included in its output. But that would only
> be true if there are upper plan nodes that are doing some projections of
> their own. The final query output will definitely not have them.

I *think* we don't even do that, because build_physical_tlist() bails
out if there's a dropped (or missing) column. Or are you thinking of
something else?

Greetings,

Andres Freund