I wrote:
> Michael Glaesemann <grzm@seespotcode.net> writes:
>> -- ERROR: could not find pathkey item to sort
> Hm ... I can reproduce that in 9.3 but it seems fine in 9.4 and HEAD.
> Don't know what's going on exactly.
Interesting --- it appears that commit
a87c729153e372f3731689a7be007bc2b53f1410 is why it works in 9.4. I had
thought that was just improving plan quality, but it seems to also prevent
this problem. I guess we'd better back-patch it.
I find that 9.1 through 9.3 fail with this example; it may be that it was
the addition of MergeAppend support that exposed the issue.
regards, tom lane