Best way to add to DB while checking for duplicates

Situation:
Day 1
Table contains 100 items of actions imported via FTP. One of the fields
in the table can be updated to reflect an assigned unit code.


Day 2
Actions that may be duplicates of the table from Day 1 (with the
exception of the updated assigned unit field) are imported for
inclusion in the Table from Day 1.

Question- What is the best way to insure that any new items are added
to the table and that no duplicates are added at the sametime?

Assistance would be appreciated.

re: Best way to add to DB while checking for duplicates

A common solution is to load your data into a staging table which has
the same structure as the destination table. You can then use a query
like this to import only new rows:

insert into
dbo.Destination (col1, col2, ...)
select
col1, col2, ...
from
dbo.Staging s
where not exists (
select *
from dbo.Destination d
where s.keycol = d.keycol)

Simon