Sequence-table association

Hi All,

I don't know if this is the right place, but I have a question about
postgres sequences. Does anyone here know if there is a way to associate a
sequence with a table (for primary keys) so that when inserts are made in
the table even without using the sequence, its nextval is automatically
updated? Even the serial datatype doesn't help much because the sequence is
not auto-updated when it is not used.

So the bottomline of my problem is to be able to choose between having the
sequence generate a number for my primary key, and providing one myself
without ever getting yelled at for trying to insert a duplicate key.

Any ideas anyone?
TIA
Vamsee Koneru.

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