insert records into a table - column as rows based on conditions

I have a table - Base_table

create table base_table (ID number,FACTOR_1 number,FACTOR_1 number,FACTOR_3 number,FACTOR_4 number,TOTAL number, J_CODE varchar2(10))

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');

ID	FACTOR_1	FACTOR_2	FACTOR_3	FACTOR_4	TOTAL	J_CODE
1	10	52	5	32	140	M1
2	null	32	24	12	311	M2
3	12	null	53	null	110	M3
4	43	45	42	3	133	M1
5	432	24	null	68	581	M2
6	null	7	98	null	196	M1

I need to insert this data into another table (FCT_T) based on certain criterias.

Also, I am trying to avaoid usage of unpivot as there are several other columns that I need to insert and manage as part of insert.

create table fct_t (id number, p_code varchar2(21), p_value number);

Logic to use -

Below values are not part of table, but needs to be used (hard-coded) in logic/criteria (perhaps CASE statements) -

M_VAL	FACT_1_CODE	FACT_2_CODE	FACT_3_CODE	FACT_4_CODE
M1	R1	R2	R3	R4
M2	R21	R65	R6	R245
M3	R1	R01	R212	R365

What I need is something similar (or any better approach available) -

insert into FCT_T values 
select id, 
case when FACTOR_1>0 and J_CODE = 'M1' then 'R1' end ,
factor_1
from base_table;

So far not able to figure out, how I can move factor column as rows, given an ID can have any number of rows from 1 to 4 based on criteria. Appreciate help here.

Partial final/expected output (FCT_T) -

ID	P_CODE	P_VALUE
1	R1	10
1	R2	52
1	R3	5
1	R4	32
2	R65	32
2	R6	24
2	R245	12

Solution

You can join the table to your codes and then UNPIVOT to convert columns into rows:

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;

db<>fiddle here