모든 PROJECT에 참여한 EMP_ID를 찾는 다음 질의의 결과는?

PROJECT PROJECT_ID P1 P2

SELECT DISTINCT p.emp_id
FROM participation p
WHERE NOT EXISTS (
  SELECT 1 FROM project pr
  WHERE NOT EXISTS (
    SELECT 1 FROM participation x
    WHERE x.emp_id = p.emp_id
      AND x.project_id = pr.project_id
  )
);