On Thu, Jul 28, 2011 at 5:36 PM, Tom Lane
<tgl@sss.pgh.pa.us> wrote:
> It also appears you cannot group on a column of type xid.
You can in 8.4 and up. Previous versions only know how to GROUP BY
sortable columns, which requires a btree opclass, which xid doesn't
have and really can't have because it doesn't have a linear ordering.
There is a hash opclass for it, though, so in versions that know how to
GROUP BY using hashing, it'll work.
:sigh: I thought I had done all the tests on my 9.0.4 testbed server too. One of
these days I hope to get the production and development servers off 8.2.
I more or less understand why xid types don't have a linear ordering from Robert Hass's tutorial at PGCON11.
So, a <> operator (either xid,xid or xid,integer) would need to be implemented using the hash opclass, correct?
(I don't have a use case for it yet, though.)
> Would adding a <> operator enable that?
No, it's pretty irrelevant ...
OK, thanks for putting up with my noobie questions.
--
Mike Nolan
