Re: BUG #15795: ERROR: could not find pathkey item to sort

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> Here is query:
> SELECT DISTINCT A._id0 as _id0, A._actual_type_name0 as _actual_type_name0
> FROM ( ( SELECT DISTINCT _id as _id0, _actual_type_name as
> _actual_type_name0, name as name0 FROM hello_world.person ) union all (
> SELECT DISTINCT _id as _id0, _actual_type_name as _actual_type_name0, name
> as name0 FROM hello_world.person)) as A WHERE ( A.name0 = A.name0 );

It's politer to provide a self-contained test case, rather than expect us
to reverse-engineer details that might be critical.

For the archives, though, this isn't hard to reproduce:

regression=# create table person(_id int, _actual_type_name text, name text);
CREATE TABLE
regression=# SELECT DISTINCT A._id0 as _id0, A._actual_type_name0 as _actual_type_name0
FROM ( ( SELECT DISTINCT _id as _id0, _actual_type_name as
_actual_type_name0, name as name0 FROM person ) union all (
SELECT DISTINCT _id as _id0, _actual_type_name as _actual_type_name0, name
as name0 FROM person)) as A WHERE ( A.name0 = A.name0 );
ERROR: could not find pathkey item to sort

Curiously, this only fails for me in 9.6 and 10, not earlier or later
branches.

regards, tom lane