Re: DROP COLUMN

Christopher Kings-Lynne wrote:
> > Uh, then what? The only idea I had was to set a static boolean
> > variable in
> > syscache.c that controls whether droppped columns are returned, and have
> > a enable/disable functions that can turn it on/off. The only problem is
> > that an elog inside a syscache lookup would leave that value set.
> >
> > My only other idea is to make a syscache that is like ATTNAME except
> > that it doesn't return a dropped column. I could probably code that up
> > if you wish.
>
> That'd be cool.
>
> I guess the thing is that either way, I will need to manually change every
> single instance where a dropped column should be avoided. So, really
> there's not much difference between me changing the SysCache search to use
> ATTNAMEUNDROPPED or whatever, or just checking the attisdropped field of the
> tuple in the same way that you must always check that attnum > 0.
>
> In fact, looking at it logically...if all the commands currently are
> required to check that they're not modifiying a system column, then why not
> add the requirement that they must also not modify dropped columns? I can
> do a careful doc search and try to make sure I've touched everything...

Makes sense. Of course, we could make a syscache that didn't return
system columns either.

Actually, the original argument for negative attno's for dropped columns
was exactly for this case, that the system column check would catch
dropped columns too, but it causes other problems that are harder to fix
so we _dropped_ the idea.

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