Insert/Update in PL/SQL - sql

Question

I have made a procedure in PL/SQL which inserts data from one table to another on basis of primary key. My procedure is working fine but i can't figure out how will i update column CODE_NUMBER of my table MAIN if primary key already exists.
Actually i want rows of MAIN table to get UPDATED when its has primary key and insert data from REGIONS when primary key does not exists.
DECLARE
variable number;
id number;
description varchar2 (100);
CURSOR C1 IS
select regions.REGION_ID variable
from regions;
BEGIN
FOR R_C1 IN C1 LOOP
BEGIN
select regions.REGION_ID,regions.REGION_NAME
into id,description
from regions
where regions.REGION_ID = R_C1.variable;
----If exists then update otherwise insert
INSERT INTO MAIN( ID, CODE_NUMBER) VALUES( id,description);
dbms_output.put_line( id ||' '|| 'Already Exists');
EXCEPTION
WHEN DUP_VAL_ON_INDEX THEN
dbms_output.put_line( R_C1.variable);
END;
END LOOP;
END;

Answer 1

There's no need to do this with PL/SQL and cursors. What you really want to do is something like this:
MERGE INTO MAIN dst
USING (
SELECT regions.REGION_ID id,
regions.REGION_NAME description
FROM regions
) src
ON src.id = dst.id
WHEN MATCHED THEN UPDATE
SET dst.code_number = src.description
WHEN NOT MATCHED THEN INSERT (id, code_number)
VALUES (src.id, src.description)
Read more about the SQL MERGE statement in the documentation

Answer 2

I can not really see a point in doing a cursor in this case. Why can't you just do it like this:
--Update the rows
UPDATE MAIN
SET ID=regions.REGION_ID,
CODE_NUMBER=regions.[description]
FROM MAIN
JOIN regions
ON MAIN.ID=regions.REGION_ID;
--Insert the new ones
INSERT INTO MAIN(ID,CODE_NUMBER)
SELECT
regions.REGION_ID,
regions.[description]
FROM
regions
WHERE NOT EXISTS
(
SELECT
NULL
FROM
MAIN.ID=regions.REGION_ID
)