create function f_employee_departments(userName..) as select * from employee_departments ed
join user_departments ud on..
where  ud.userName  = userName 

create function f_employee(userName..) as select * from employee e
join f_employee_departments(userName) ed on e.employee_id = ed.employee_id
  

select * from f_employee('UserName') where employee_id = 123

select * from employee where employee_id = 123 

create or replace view vw_employee_deparment as 
select ed.* 
from employee_departemnt ed
join user_departments ud on ed.department_id = ud.department_id and (ed.userName = current_setting('custom.user', true) or current_setting('custom.is_admin')=1)

create table departments(depId int primary key );

do $$
begin
  for i in 1..30 loop
    insert into departments(depId) values(i);
  end loop;
end $$;

create table user_privs
(
	user_name varchar(30),
	dep_id int
		constraint user_privs_departments_depid_fk
			references departments,
	constraint user_privs_pk
		primary key (user_name, dep_id)
);

do $$
begin
  for i in 1..30 loop
    insert into user_privs(user_name, dep_id)
    values ('user'||(i%15)::text, i);
  end loop;
end;
$$

create table employee
(
	employee_id int not null
		constraint employee_pk
			primary key,
	dep_id int not null
		constraint employee_fk
			references departments
);


do $$
begin
  for i in 1..1000000 loop
    insert into employee(employee_id, dep_id)
    values (i, i%30+1);
  end loop;
end;
$$

alter table employee enable row level security;

create policy pol_emp on employee
using (dep_id in (select up.dep_id from user_privs up where up.user_name = current_user));


create user user1 with login password '1';
grant all privileges  on all tables in schema dk to user1;

explain analyze verbose select * from dk.employee where employee_id = 14505;

QUERY PLAN
Index Scan using employee_pk on dk.employee  (cost=21.54..29.56 rows=1 width=8) (actual time=0.061..0.062 rows=1 loops=1)
  Output: employee.employee_id, employee.dep_id
  Index Cond: (employee.employee_id = 14505)
  Filter: (hashed SubPlan 1)
  SubPlan 1
    ->  Seq Scan on dk.user_privs up  (cost=0.00..21.10 rows=4 width=4) (actual time=0.010..0.016 rows=2 loops=1)
          Output: up.dep_id
          Filter: ((up.user_name)::text = CURRENT_USER)
          Rows Removed by Filter: 28
Planning Time: 0.150 ms
Execution Time: 0.099 ms

explain analyze verbose select * from dk.employee where dep_id = 16

QUERY PLAN
Gather  (cost=1021.11..13277.81 rows=15817 width=8) (actual time=0.516..177.470 rows=33333 loops=1)
  Output: employee.employee_id, employee.dep_id
  Workers Planned: 2
  Workers Launched: 2
  ->  Parallel Seq Scan on dk.employee  (cost=21.11..10696.11 rows=6590 width=8) (actual time=0.017..46.692 rows=11111 loops=3)
        Output: employee.employee_id, employee.dep_id
        Filter: ((hashed SubPlan 1) AND (employee.dep_id = 16))
        Rows Removed by Filter: 322222
        Worker 0:  actual time=0.002..0.002 rows=0 loops=1
        Worker 1:  actual time=0.002..0.002 rows=0 loops=1
        SubPlan 1
          ->  Seq Scan on dk.user_privs up  (cost=0.00..21.10 rows=4 width=4) (actual time=0.010..0.017 rows=2 loops=1)
                Output: up.dep_id
                Filter: ((up.user_name)::text = CURRENT_USER)
                Rows Removed by Filter: 28
Planning Time: 0.202 ms
Execution Time: 178.211 ms