Unique record Identifier?

Hi all,

I'm busy writing an application using PostGreSQL and PHP, so my db reads are
'stateless' and I don't know at record 'write' time which record I have read
to begin with. The records I have, have an index, most tables do have a
unique index but the index values could get changed during an update. In
order to be able to re-read a record, I would like to use some unique
identifier of that record, like a unique db-wide rec-id. Does this exist in
PostGres and if so, how do I access it?

Best regards,
Chris


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