SQL join on values not in table primary keys

Question

I need to get the batch ids that are not assigned to a user. I had this select statement:

SELECT batch.id 
FROM batch 
WHERE (SELECT batch.id 
       FROM batch 
       JOIN user 
       WHERE batch.id = user.batch_id) "+ "!= batch.id 
  AND submitted = 0 
  AND batch.project_id = ?

It worked except when no batch_ids are assigned to users. And I can't just add another column to batch to, I tried but it requires way to much work. Is there a better way to do this? I don't care about optimization I just need it to work.

CREATE TABLE batch
(
    id integer not null primary key autoincrement,
    filepath varchar(255) not null,
    project_id integer not null,
    submitted boolean not null
);

CREATE TABLE user
(
    id integer not null primary key autoincrement,
    first_name varchar(255) not null,
    last_name varchar(255) not null,
    user_name varchar(255) not null,
    password varchar(255) not null,
    num_records integer not null,
    email varchar(255) not null,
    batch_id integer not null
);

Answer 1

SELECT b.id
FROM batch b
LEFT JOIN user u ON u.batch_id = b.id
WHERE u.id IS NULL
  AND b.submitted = 0
  AND b.project_id = ?

Answer 2

This is a classic type of query which can be written in two ways

select batch.id
from batch
left join user on user.batch_id = batch.id
where user.id is null
and batch.submitted = 0 
and batch.project_id = ?

or

select batch.id
from batch
where not exists (select 1 from user
where user.batch_id = batch.id)
and batch.submitted = 0 
and batch.project_id = ?