sql - ORA-01722: 副問合せで無効な数値がスローされました

Question

次のようなクエリがあります。

SELECT 
  WAH.ALERT_KEY AS ALERT_KEY, 
  TRUNC(WAH.EVENT_DATE) AS ALERT_DATE, 
  WAH.AT_DATASOURCE_ID AS DATA_SOURCE_ID, 
  WAH.CHECK_DEFINITION_ID AS CHECK_ID, 
  OU.ID AS ORGUNIT_ID, 
  USR.ID AS USER_ID, 
  GRP.ID AS GROUP_ID, 
  CUS.SOURCE_SYSTEM AS SOURCE_SYTEM 
FROM 
  WLM_ALERT_HEADER WAH, 
  CHECK_DEFINITION CD, 
  ORGANIZATION_UNITS OU, 
  USERS USR, 
  GROUPS GRP, 
  CUSTOMERS CUS, 
  WORKFLOW_WORKITEM WW 
WHERE 
  WAH.ALERT_KEY in (
    select 
      ENTITY_KEY 
    from 
      WORKFLOW_WORKITEM ww 
    where 
      ww.STATUS_ID in (
        select 
          ID 
        from 
          WORKFLOW_STATUSES ws 
        where 
          ws.CODE IN (
            'S_GE_WLM_WL_001', 'S_GE_WLM_WL_002', 
            'S_GE_WLM_WL_003', 'S_GE_WLM_WL_004', 
            'S_GE_WLM_WL_007', 'S_GE_WLM_WL_010'
          ) 
          and ww.ORGUNIT_ID in (
            select 
              ou.ID 
            from 
              ORGANIZATION_UNITS ou 
            where 
              ou.ID = (
                select 
                  cus.ORGUNIT_ID 
                from 
                  CUSTOMERS cus 
                where 
                  cus.CUSTOMER_ID = wah.CUSTOMER_ID
              )
          )
      ) 
  ) 
  AND WAH.CHECK_DEFINITION_ID = CD.ID 
  AND USR.ID = WW.ASSIGNED_TO 

  AND GRP.ID IN (
    select 
      GROUP_ID 
    from 
      USER_GROUP_RELATIONS 
    where 
      USER_ID = USR.ID
  ) 
  AND WW.ENTITY_NAME = 'WLM Alert';

これらの2行を配置しない限り、上記のクエリに対してORA-01722がスローされます。

AND WAH.CHECK_DEFINITION_ID = CD.ID 
AND USR.ID = WW.ASSIGNED_TO

サブクエリ WAH.ALERT_KEY の右括弧内

ただし、これらの 2 行はサブクエリの一部ではないため、この方法ではいけません。サブクエリのどのフィールドが変換の失敗について不平を言っているのだろうか。