update your target table from that staging table using the MERGE command
Check out the MSDN docs and a great blog post on how to use the MERGE command.
Basically, you create a link between your actual data table and the staging table on a common criteria (e.g. a common primary key), and then you can define what to do when
the rows match, e.g. the row exists in both the source and the target table --> typically you'd either update some fields, or just ignore it all together
the row from the source doesn't exist in the target --> typically a case for an INSERT
You would have a MERGE statement something like this:
MERGE TargetTable AS t
USING SourceTable AS src
ON t.PrimaryKey = src.PrimaryKey
WHEN NOT MATCHED THEN
INSERT (list OF fields)
VALUES (list OF values)
WHEN MATCHED THEN
SET (list OF SET statements)
Of course, the ON clause can be much more involved if needed. And of course, your WHEN statements can also be more complex, e.g.
WHEN MATCHED AND (some other condition) THEN ......
and so forth.
MERGE is a very powerful and very useful new command in SQL Server 2008 - use it, if you can!