I hope this info can help you with your 2nd
question.

Off the top of my head there are aleast 3 ways
to check the table before you insert a new record.

way one) would be to define a unique constraint
on this table in the DBMS. This will prevent any
insertion of a record that is a duplicate.

way two) would be to define a before insert trigger
and have this trigger check for a duplicate.

way three) execute the query select count(*) into n from ...
and if n > 0 then the record exist.

--
Its like a dog that can sing and dance.
It's remarkable because it can do it.
Not that it can do it well.

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