Oracle 11g Release 2

with 
    developer(id, name) as (
        select 1, 'Dev1' from dual union all
        select 2, 'Dev2' from dual union all
        select 3, 'Dev3' from dual ),
    customer (id, name) as (select 1, 'Cust1' from dual),
    project(id, customer_id, name, type, start_date, end_date) as (
        select 1, 1, 'P1', 2, date '2018-04-16', date '2018-06-02' from dual union all
        select 2, 0, 'P2', 0, date '2017-04-16', date '2017-04-20' from dual union all
        select 3, 1, 'P3', 0, date '2018-11-20', null from dual ),
    task(id, name, project_id, type, start_date, end_date) as (
        select 1, 'T1', 1, 0, date '2018-06-01', date '2018-06-02' from dual union all
        select 2, 'T2', 2, 0, date '2017-04-17', date '2017-04-20' from dual union all
        select 3, 'T3', 3, 0, date '2018-11-21', null from dual ),
    developer_task(dev_id, task_id) as (
        select 1, 1 from dual union all
        select 2, 2 from dual union all
        select 3, 2 from dual )

select p.id project_id, p.name project_name, d.name dev_name, 
           case p.customer_id when 0 then 'Internal' else c.name end cust_name
      from project p
        left join customer c on c.id = p.customer_id
        join task t on t.project_id = p.id
        join developer_task dt on dt.task_id = t.id
        join developer d on d.id = dt.dev_id
      where p.end_date is not null

PROJECT_ID	PROJECT_NAME	DEV_NAME	CUST_NAME
1	P1	Dev1	Cust1
2	P2	Dev2	Internal
2	P2	Dev3	Internal

with 
    developer(id, name) as (
        select 1, 'Dev1' from dual union all
        select 2, 'Dev2' from dual union all
        select 3, 'Dev3' from dual ),
    customer (id, name) as (select 1, 'Cust1' from dual),
    project(id, customer_id, name, type, start_date, end_date) as (
        select 1, 1, 'P1', 2, date '2018-04-16', date '2018-06-02' from dual union all
        select 2, 0, 'P2', 0, date '2017-04-16', date '2017-04-20' from dual union all
        select 3, 1, 'P3', 0, date '2018-11-20', null from dual ),
    task(id, name, project_id, type, start_date, end_date) as (
        select 1, 'T1', 1, 0, date '2018-06-01', date '2018-06-02' from dual union all
        select 2, 'T2', 2, 0, date '2017-04-17', date '2017-04-20' from dual union all
        select 3, 'T3', 3, 0, date '2018-11-21', null from dual ),
    developer_task(dev_id, task_id) as (
        select 1, 1 from dual union all
        select 2, 2 from dual union all
        select 3, 2 from dual )

select id, name, nvl(cnt, 0) cnt
      from developer d
      left join (
        select dev_id, count(1) cnt
          from project p
            join task t on t.project_id = p.id
            join developer_task dt on dt.task_id = t.id
          where p.type = 2 
            and t.start_date <= trunc(sysdate, 'year') - 1 
            and (add_months(trunc(sysdate, 'year'), -12) <= t.end_date or t.end_date is null)
          group by dev_id) t on t.dev_id = d.id

ID	NAME	CNT
1	Dev1	1
3	Dev3	0
2	Dev2	0

with 
    developer(id, name) as (
        select 1, 'Dev1' from dual union all
        select 2, 'Dev2' from dual union all
        select 3, 'Dev3' from dual ),
    customer (id, name) as (select 1, 'Cust1' from dual),
    project(id, customer_id, name, type, start_date, end_date) as (
        select 1, 1, 'P1', 2, date '2018-04-16', date '2018-06-02' from dual union all
        select 2, 0, 'P2', 0, date '2017-04-16', date '2017-04-20' from dual union all
        select 3, 1, 'P3', 0, date '2018-11-20', null from dual ),
    task(id, name, project_id, type, start_date, end_date) as (
        select 1, 'T1', 1, 0, date '2018-06-01', date '2018-06-02' from dual union all
        select 2, 'T2', 2, 0, date '2017-04-17', date '2017-04-20' from dual union all
        select 3, 'T3', 3, 0, date '2018-11-21', null from dual ),
    developer_task(dev_id, task_id) as (
        select 1, 1 from dual union all
        select 2, 2 from dual union all
        select 3, 2 from dual )
select * 
  from developer 
  where id not in (
    select dev_id 
      from project p 
      join task t on t.project_id = p.id 
      join developer_task dt on dt.task_id = t.id
      where p.type = 0)

ID	NAME
1	Dev1