Using IF and other conditions in T-SQL (trying to import data from Oracle using SQL Server SSIS)
assuming you can see the oracle table from your SQL Server

INSERT INTO SQLTable( ID, field2 )
SELECT ID,
       field2
FROM OracleTable o
WHERE NOT EXISTS( SELECT NULL FROM SQLTable s WHERE s.ID = o.ID )


this is just the simple SQL for inserts. I have not used SSIS so YMMV