Hans-Jürgen Schönig <postgres@cybertec.at> writes:
> I have seen that a bug related to duplicated keys is in 7.4rc2. As far
> as I have seen a bug like that has already been discovered during the
> 7.3 era. Is this bug going to be fixed?
We do not have, and never have had, deferred unique constraints, which
is what would be needed to make this UPDATE work safely. As-is, you
update the '5' entry to '4', and this fails if the '4' row hasn't been
updated yet, which depends on the order the rows happen to be visited
in.
It's on the TODO list but don't hold your breath ...
regards, tom lane