从你在评论中的解释来看，我相信这就是你要找的。我将使用union操作符把两个相似的数据集组合在一起。一个是你对PI和PD的原始查询，另一个是你的 predicate 的逆。在下面的查询中，我将把NULL赋为pers的值，作为默认值。

SELECT DISTINCT
  PROPOSAL_NUMBER, 
  FIRST_VALUE(PROP_PERSON_ROLE_ID) OVER (PARTITION BY PROPOSAL_NUMBER ORDER BY PROPOSAL_NUMBER), 
  FIRST_VALUE(FULL_NAME) OVER (PARTITION BY PROPOSAL_NUMBER ORDER BY PROPOSAL_NUMBER), 
  FIRST_VALUE(HOME_UNIT) OVER (PARTITION BY PROPOSAL_NUMBER ORDER BY PROPOSAL_NUMBER)
FROM
((
SELECT eps.PROPOSAL_NUMBER,
       pers.PROP_PERSON_ROLE_ID,
       pers.FULL_NAME,       
       pers.HOME_UNIT
       FROM EPS_PROPOSAL eps
       LEFT JOIN EPS_PROP_PERSON pers ON eps.PROPOSAL_NUMBER = pers.PROPOSAL_NUMBER
       WHERE (pers.PROP_PERSON_ROLE_ID = 'PI' OR 
              pers.PROP_PERSON_ROLE_ID = 'PD' OR 
              pers.PROP_PERSON_ROLE_ID IS NULL)
)
UNION
(
SELECT eps.PROPOSAL_NUMBER,
       NULL as PROP_PERSON_ROLE_ID,
       NULL as FULL_NAME,       
       NULL as HOME_UNIT
       FROM EPS_PROPOSAL eps
       LEFT JOIN EPS_PROP_PERSON pers ON eps.PROPOSAL_NUMBER = pers.PROPOSAL_NUMBER
       WHERE (pers.PROP_PERSON_ROLE_ID != 'PI' AND
              pers.PROP_PERSON_ROLE_ID != 'PD' AND
              pers.PROP_PERSON_ROLE_ID IS NOT NULL)
))

将WHERE过滤器移至JOIN条件：

SELECT eps.PROPOSAL_NUMBER,
       pers.PROP_PERSON_ROLE_ID,
       pers.FULL_NAME,       
       pers.HOME_UNIT
FROM   EPS_PROPOSAL eps
       FULL OUTER JOIN EPS_PROP_PERSON pers
       ON (   eps.PROPOSAL_NUMBER = pers.PROPOSAL_NUMBER
          AND (  pers.PROP_PERSON_ROLE_ID IN ( 'PI', 'PD' )
              OR pers.PROP_PERSON_ROLE_ID IS NULL)
          );

或者，对于LEFT JOIN：

SELECT eps.PROPOSAL_NUMBER,
       pers.PROP_PERSON_ROLE_ID,
       pers.FULL_NAME,       
       pers.HOME_UNIT
FROM   EPS_PROPOSAL eps
       LEFT JOIN EPS_PROP_PERSON pers
       ON (   eps.PROPOSAL_NUMBER = pers.PROPOSAL_NUMBER
          AND (  pers.PROP_PERSON_ROLE_ID IN ( 'PI', 'PD' )
              OR pers.PROP_PERSON_ROLE_ID IS NULL)
          );

如果使用WHERE过滤器，则将执行JOIN，然后将过滤掉不匹配的行，这将同时排除pers和eps中的行（因为您已经连接了表）。如果在连接中应用过滤器，则pers表将在连接之前被过滤，并且eps中的所有行都将被返回。