"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
> OK, I've been looking at Hiroshi's implementation. It's basically
> semantically equivalent to mine from what I can see so far. The only
> difference really is in how the dropped columns are marked.
True enough, but that's not a trivial difference. The problem with
Hiroshi's implementation is that there's no longer a close tie between
pg_attribute.attnum and physical positions of datums in tuples. I think
that that's going to affect a lot of low-level code, and that he hasn't
found all of it.
Keeping the attisdropped marker separate from attnum is logically
cleaner, and IMHO much less likely to lead to trouble down the road.
We should not allow ourselves to put too much weight on the fact that
some clients use "attnum > 0" as a filter for attributes that they
(think they) need not pay attention to. That's only a historical
artifact, and it's far from clear that it will keep those clients
out of trouble anyway.
regards, tom lane