Insert/Update in PL/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
    )