PostgreSQL : 8.2
Operating system:  fedora RC4

--------

create table a (a1 integer);
create table b (b1 integer);

insert into a (a1) values (1);
insert into a (a1) values (2);
select a1 from b;

ERROR:  column "a1" does not exist at character 8

but :
select a1 from a where a1 not in (select a1 from b);

 a1
----
  1
  2
(2 rows)


when b is not empty :

insert into b (b1) values (1);

select a1 from b;
ERROR:  column "a1" does not exist at character 8

but :
select a1 from a where a1 not in (select a1 from b);
 a1
----
(0 rows)

select a1 from a where a1 in (select a1 from b);
 a1
----
  1
  2
(2 rows)

Attachment: smime.p7s
Description: S/MIME Cryptographic Signature

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