Question

Excerpt fro pgsql 8.4 docs : ” […]a column constraint is only a notational convenience for use when the constraint only affects one column.”
How is this valid sql then?

DROP TABLE IF EXISTS test;
CREATE TABLE test(
id integer CONSTRAINT PK_test PRIMARY KEY  CONSTRAINT nenull NOT NULL CHECK (id3>=id2) 
--the check constraint affects two columns none of which is id
,id2 integer 
, id3 integer
);

the excerpt seems to apply only to PRIMARY KEY and FOREIGN KEY constraints which should only affect the column on the same line where the constraints are declarated as Catcall has stated

Answer 1

Elsewhere in the docs . . .

We say that the first two constraints are column constraints, whereas
the third one is a table constraint because it is written separately
from any one column definition. Column constraints can also be written
as table constraints, while the reverse is not necessarily possible,
since a column constraint is supposed to refer to only the column
it is attached to. (PostgreSQL doesn’t enforce that rule, but you
should follow it if you want your table definitions to work with other
database systems.)