Oracle 21c

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create table base_table (
  ID number,
  FACTOR_1 number,
  FACTOR_2 number,
  FACTOR_3 number,
  FACTOR_4 number,
  TOTAL number,
  J_CODE varchar2(10)
)
create table fct_t (
  id number,
  p_code varchar2(21),
  p_value number
);
BEGIN
insert into base_table values (1,10,52,5,32,140,'M1');
insert into base_table values (2,null,32,24,12,311,'M2');
insert into base_table values (3,12,null,53,null,110,'M3');
insert into base_table values (4,43,45,42,3,133,'M1');
insert into base_table values (5,432,24,null,68,581,'M2');
insert into base_table values (6,null,7,98,null,196,'M1');
END;
/
1 rows affected

INSERT INTO fct_t (id, p_code, p_value)
WITH codes (M_VAL, FACT_1_CODE, FACT_2_CODE, FACT_3_CODE, FACT_4_CODE) AS (
  SELECT 'M1', 'R1',  'R2',  'R3',   'R4'   FROM DUAL UNION ALL
  SELECT 'M2', 'R21', 'R65', 'R6',   'R245' FROM DUAL UNION ALL
  SELECT 'M3', 'R1',  'R01', 'R212', 'R365' FROM DUAL
)
SELECT id, p_code, p_value
FROM   base_table b
       INNER JOIN codes c
       ON (b.j_code = c.m_val)
UNPIVOT (
  (p_code, p_value)
  FOR factor IN (
    (fact_1_code, factor_1) AS 1,
    (fact_2_code, factor_2) AS 2,
    (fact_3_code, factor_3) AS 3,
    (fact_4_code, factor_4) AS 4
  )
)
WHERE p_value IS NOT NULL;
18 rows affected