einfach beim COPY angeben, daß für diese Spalte keine Daten kommen:
test=*# create table bla (id serial primary key, val int);
CREATE TABLE
test=*# copy bla(val) from stdin;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself, or an EOF signal.
>> 10
>> 23
>> 23
>> 12
>> 22
>> \.
COPY 5
test=*# select * from bla;
id | val
----+-----
1 | 10
2 | 23
3 | 23
4 | 12
5 | 22
(5 rows)
test=*#