title: psycopg2.copy_expert - insert only new data
body: <p>I am using psycopg2.copy_expert to copy data from CSV to PostgreSQL DB. I run this every day and I want only the new data to be inserted. If data is already present then no action must be perfomed. Is there a way to leverage copy_expert function to do this out of the box or do I have code his logic myself and create a new CSV file that contains only the delta changes?</p>
  
  <pre><code>copy_sql = """
             COPY %s FROM stdin WITH CSV HEADER
             DELIMITER as ','
             """
  f = open(f"{file_path}", 'r', encoding="utf-8")
  cur.copy_expert(sql=copy_sql % table_name, file=f)
  </code></pre>