# original query using IN
select e.deptno,
  e.deptno IN (select deptno from v)
from e;

# rewritten to use just (outer) joins and 2-valued logic
select e.deptno,
  case
  when ct.c = 0 then false
  when dt.i is not null then true
  when e.deptno is null or ct.ck < ct.c then null
  else false
  end
from e
cross join (select count(*) as c, count(deptno) as ck from v) as ct
left join (select distinct deptno, true as i from v) as dt on e.deptno = dt.deptno;

create table e(deptno int, ename varchar(5));
insert into e values (10, 'Alice');
insert into e values (null, 'Bob');
create table d(deptno int, dname varchar(10));
insert into d values (10, 'Sales');
insert into d values (20, 'Marketing');
insert into d values (null, 'Null');
select * from d where deptno not in (select deptno from e);
 deptno | dname
--------+-------
(0 rows)

select deptno,
  deptno not in (select deptno from e)
from d;

 deptno | ?column?
--------+----------
     10 | FALSE
     20 | UNKNOWN
   NULL | UNKNOWN

(3 rows)

with
t1(x) as (select * from  (values (1),(2), (case when 1 = 1 then null else 3 end)) as t(x)),
t2(x) as (select * from  (values (1),(case when 1 = 1 then null else 3 end)) as t(x))
select t1.x, (t1.x not in (select t2.x from t2)) from t1;
   x | ?column? 
-----+----------
   1 | FALSE
   2 | UNKNOWN
NULL | UNKNOWN
(3 rows)