My Requirement and  approach 1

External Table

  CREATE TABLE "SS_REPO"."TH_FREQ_INV_PROF_CHNG_XT" 
   (	"BRANCH" VARCHAR2(100 BYTE), 
	"RC" VARCHAR2(100 BYTE), 
	"AO" VARCHAR2(100 BYTE), 
	"AO_NAME" VARCHAR2(100 BYTE), 
	"CUSTOMER" VARCHAR2(100 BYTE), 
	"CUSTOMER_NAME" VARCHAR2(100 BYTE), 
	"RELATIONSHIP" VARCHAR2(100 BYTE), 
	"RELATIONSHIP_TITLE" VARCHAR2(100 BYTE), 
	"RISK_PROFILE" VARCHAR2(100 BYTE), 
	"LATEST_RISK_PROFILE" VARCHAR2(100 BYTE), 
	"LATEST_RISK_PROFILE_DATE" DATE, 
	"PREVIOUS_RISK_PROFILE" VARCHAR2(100 BYTE), 
	"PREVIOUS_RISK_PROFILE_DATE" DATE, 
	"MONTH_ID" VARCHAR2(100 BYTE), 
	"ROW_NUM" VARCHAR2(100 BYTE)
   ) 
   ORGANIZATION EXTERNAL 
    ( TYPE ORACLE_LOADER
      DEFAULT DIRECTORY "ETL_WORKING"
      ACCESS PARAMETERS
      ( RECORDS DELIMITED BY '#$/' 
    LOGFILE ETL_ORA_LOG:'th_rdsinv8_freq_inv_prf_chg.log' 
    BADFILE ETL_ORA_LOG:'th_rdsinv8_freq_inv_prf_chg.bad' 
    DISCARDFILE ETL_ORA_LOG:'th_rdsinv8_freq_inv_prf_chg.disc' 
    DATE_CACHE 0 FIELDS TERMINATED BY '~' LRTRIM 
    MISSING FIELD VALUES ARE NULL ( 
BRANCH	char(100),
RC	char(100),
AO	char(100),
AO_NAME	char(100),
CUSTOMER	char(100),
CUSTOMER_NAME	char(100),
RELATIONSHIP	char(100),
RELATIONSHIP_TITLE	char(100),
RISK_PROFILE	char(100),
LATEST_RISK_PROFILE	char(100),
LATEST_RISK_PROFILE_DATE	char(20) date_format date  mask 'mmddyyyy hh24:mi:ss',
PREVIOUS_RISK_PROFILE	char(100),
PREVIOUS_RISK_PROFILE_DATE	char(20) date_format date  mask 'mmddyyyy hh24:mi:ss',
MONTH_ID	char(100),
ROW_NUM	char(12)
)                )
      LOCATION
       ( "ETL_WORKING":'th_rdsinv8_freq_inv_prf_chg.ssf'
       )
    )
   REJECT LIMIT UNLIMITED ;

Staging table with virtual column

  CREATE TABLE "SS_REPO"."TH_FREQ_INV_PROF_CHNG_STG" 
   (	"MONTH_ID" VARCHAR2(50 BYTE), 
	"BRANCH" VARCHAR2(100 BYTE), 
	"RC" VARCHAR2(100 BYTE), 
	"AO" VARCHAR2(100 BYTE), 
	"AO_NAME" VARCHAR2(100 BYTE), 
	"CUSTOMER" VARCHAR2(100 BYTE), 
	"CUSTOMER_NAME" VARCHAR2(100 BYTE), 
	"RELATIONSHIP" VARCHAR2(100 BYTE), 
	"RELATIONSHIP_TITLE" VARCHAR2(100 BYTE), 
	"RISK_PROFILE" VARCHAR2(100 BYTE), 
	"LATEST_RISK_PROFILE" VARCHAR2(100 BYTE), 
	"LATEST_RISK_PROFILE_DATE" DATE, 
	"PREVIOUS_RISK_PROFILE" VARCHAR2(100 BYTE), 
	"PREVIOUS_RISK_PROFILE_DATE" DATE, 
	"ROW_NUM" VARCHAR2(100 BYTE), 
	"UPDATED_DATE" DATE, 
	"PARTY_KEY" VARCHAR2(150 BYTE) GENERATED ALWAYS AS ('764'||"CUSTOMER") VIRTUAL VISIBLE , 
	"NEW_RISK_PROFILE" VARCHAR2(500 BYTE) GENERATED ALWAYS AS ( REGEXP_REPLACE ("LATEST_RISK_PROFILE",'[^0-9]')) VIRTUAL VISIBLE , 
	"LAST_RISK_PROFILE" VARCHAR2(500 BYTE) GENERATED ALWAYS AS ( REGEXP_REPLACE ("PREVIOUS_RISK_PROFILE",'[^0-9]')) VIRTUAL VISIBLE , 
	"RELATIONSHIP_KEY" VARCHAR2(150 BYTE) GENERATED ALWAYS AS ('764'||"RELATIONSHIP") VIRTUAL VISIBLE , 
	"ERROR_FLG" CHAR(1 BYTE), 
	"SOURCE_ID" VARCHAR2(50 BYTE) GENERATED ALWAYS AS ('TH_RDSINV8') VIRTUAL VISIBLE , 
	"EMPLOYEE_KEY" VARCHAR2(100 BYTE), 
	"BRANCH_KEY" VARCHAR2(100 BYTE), 
	"ACCOUNT_KEY" VARCHAR2(100 BYTE)
   ) ;

My view 

  CREATE OR REPLACE FORCE VIEW "SS_REPO"."TH_FREQ_INV_PROF_CHNG_VW" ("AO", "AO_NAME", "BRANCH", "CUSTOMER", "CUSTOMER_NAME", "LATEST_RISK_PROFILE", "LATEST_RISK_PROFILE_DATE", "MONTH_ID", "PREVIOUS_RISK_PROFILE", "PREVIOUS_RISK_PROFILE_DATE", "RC", "RELATIONSHIP", "RELATIONSHIP_TITLE", "RISK_PROFILE", "ROW_NUM", [b]"EMPLOYEE_KEY", "BRANCH_KEY")[/b] AS 
  WITH ext_data AS
  (SELECT a.AO,
    a.AO_NAME,
    a.BRANCH,
    a.CUSTOMER,
    a.CUSTOMER_NAME,
    a.LATEST_RISK_PROFILE,
    a.LATEST_RISK_PROFILE_DATE,
    a.MONTH_ID,
    a.PREVIOUS_RISK_PROFILE,
    a.PREVIOUS_RISK_PROFILE_DATE,
    a.RC,
    a.RELATIONSHIP,
    a.RELATIONSHIP_TITLE,
    a.RISK_PROFILE,
    a.ROW_NUM,
  [b]  b.employee_key,
    d.branch_key  [/b]
  FROM ss_repo.TH_FREQ_INV_PROF_CHNG_XT a
LEFT JOIN ss_repo.party_info c
ON (('764'||a.CUSTOMER) = c.party_key)
LEFT JOIN ss_repo.rm_ao_geid b
ON ( b.rc_ao_code = c.rm)
LEFT JOIN ss_repo.employee d
ON (b.employee_key =d.employee_key)
  )
SELECT AO,
  AO_NAME,
  BRANCH,
  CUSTOMER,
  CUSTOMER_NAME,
  LATEST_RISK_PROFILE,
  LATEST_RISK_PROFILE_DATE,
  MONTH_ID,
  PREVIOUS_RISK_PROFILE,
  PREVIOUS_RISK_PROFILE_DATE,
  RC,
  RELATIONSHIP,
  RELATIONSHIP_TITLE,
  RISK_PROFILE,
  ROW_NUM,
  employee_key,
  branch_key
FROM ext_data;

Approach 2