Samed YILDIRIM <samed@reddoc.net> writes:
> Hi Teja,
> Your columns are varchar. They may seem the same to you due to the tool you
> use. But, it doesn't mean they are identical. There can be leading or
> trailing spaces.
Another thing I'm wondering about is index corruption due to an
operating-system upgrade that changed string sort ordering.
Nothing might be obviously wrong right after the upgrade, but
index searches would probably fail to find existing entries,
which could lead to not rejecting duplicate entries.
This is, sadly, not at all hypothetical or uncommon.
There's some info about this hazard at:
https://wiki.postgresql.org/wiki/Locale_data_changes
regards, tom lane