INSERT locking order

[Matthew Woodcraft]

In an INSERT, are the rows guaranteed to be inserted in the order that
the source query returns its rows, for locking purposes?

For example, if have

 CREATE TABLE foo (
   foo_id INTEGER,
   PRIMARY KEY (foo_id)
 );

and I run two concurrent copies of

 INSERT INTO foo (SELECT n FROM ... ORDER BY n);

is there any guarantee that I'll get a unique constraint violation
rather than a deadlock?

-M-