Re: DISTINCT is not quite distinct

Florian Weimer <fweimer@bfk.de> writes:
> I run this innocent query
> CREATE TABLE foo AS SELECT DISTINCT bar FROM baz ORDER BY bar;
> and the resulting table contains duplicate rows. 8-(

> According to EXPLAIN, an index scan on the bar column is used (using
> the underlying B-tree index).

Do you mean an indexscan followed immediately by a Unique node?  If
so, yeah, that would depend entirely on correct ordering of the
indexscan output to produce distinct results.

> If I drop the DISTINCT, the output is not correctly ordered, either.
> Perhaps this is an index corruption issue?  The hardware itself seems
> fine.

Perhaps.  Do you want to save off a physical copy of the index and then
try REINDEXing?  If that fixes it, I'd be interested to compare the two
versions of the index.

            regards, tom lane