gistfile1.sql

CREATE TEMPORARY TABLE foo_staging LIKE FOO;
-- replace with bulk insert if you like
\copy into foo_staging [...]

INSERT INTO foo
	SELECT
		foo_staging.*
	FROM
		foo_staging
		LEFT JOIN foo USING (key, columns, here)
	WHERE
		foo.key IS NULL
		AND foo.columns IS NULL
		AND foo.here IS NULL;