Oracle 18c

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create table DATA_IMPORT (LEARNER_ID number, USER_ID varchar2(30), ERROR_FLAG varchar2(1), IMPORT_NOTIFICATION varchar2(200));
DECLARE
   CURSOR C_DUPLICATE_IMPORT_IDS
   IS
        SELECT COUNT (D.LEARNER_ID), D.LEARNER_ID
          FROM DATA_IMPORT D
--         WHERE     D.USER_ID IN (SELECT S.OSUSER
--                                   FROM V$SESSION S
--                                  WHERE S.SID IN (SELECT DISTINCT V.SID
--                                                    FROM V$MYSTAT V))
-- sys views not visible here
WHERE 1=1
               AND D.ERROR_FLAG = 'N'
-- shoould be NOT NULL; but redundant
--               AND D.LEARNER_ID <> NULL
        HAVING COUNT (D.LEARNER_ID) > 1
      GROUP BY D.LEARNER_ID;

   V_FOUND BOOLEAN := FALSE;
   V_DUPLICATE_IMPORT_IDS   C_DUPLICATE_IMPORT_IDS%ROWTYPE;
BEGIN
   OPEN C_DUPLICATE_IMPORT_IDS;

   LOOP
      FETCH C_DUPLICATE_IMPORT_IDS INTO V_DUPLICATE_IMPORT_IDS;

      EXIT WHEN C_DUPLICATE_IMPORT_IDS%NOTFOUND;

      UPDATE DATA_IMPORT D
         SET D.ERROR_FLAG = 'Y'
       WHERE D.LEARNER_ID = V_DUPLICATE_IMPORT_IDS.LEARNER_ID;

      UPDATE DATA_IMPORT D
         SET D.IMPORT_NOTIFICATION =
                   'DUPLICATE LEARNER_ID IDENTIFIED ('
                || V_DUPLICATE_IMPORT_IDS.LEARNER_ID
                || ').  LEARNER_IDS ERROR_FLAG SET, THIS CASE WILL NOT IMPORT UNTIL CORRECTED.'
       WHERE D.LEARNER_ID = V_DUPLICATE_IMPORT_IDS.LEARNER_ID;

      DBMS_OUTPUT.PUT_LINE (
            'THE FOLLOWING LEARNER WAS IDENTIFIED AS A DUPLICATE '
         || V_DUPLICATE_IMPORT_IDS.LEARNER_ID);

      V_FOUND := TRUE;
   END LOOP;

   CLOSE C_DUPLICATE_IMPORT_IDS;

   IF NOT V_FOUND THEN
      DBMS_OUTPUT.PUT_LINE (
         CHR (10)
         || 'THERE ARE NO DUPLICATE LEARNER_IDS WITHIN THIS UPLOAD.');
   END IF;

   DBMS_OUTPUT.PUT_LINE (CHR (10) || 'STEP 1 COMPLETED');
   COMMIT;
END;
/
1 rows affected

dbms_output:

THERE ARE NO DUPLICATE LEARNER_IDS WITHIN THIS UPLOAD.

STEP 1 COMPLETED

insert into DATA_IMPORT (LEARNER_ID, ERROR_FLAG)
select 1, 'N' from dual
union all
select 2, 'N' from dual
union all
select 2, 'N' from dual
union all
select 3, 'Y' from dual
union all
select null, 'N' from dual
union all
select null, 'N' from dual;
6 rows affected

DECLARE
   CURSOR C_DUPLICATE_IMPORT_IDS
   IS
        SELECT COUNT (D.LEARNER_ID), D.LEARNER_ID
          FROM DATA_IMPORT D
--         WHERE     D.USER_ID IN (SELECT S.OSUSER
--                                   FROM V$SESSION S
--                                  WHERE S.SID IN (SELECT DISTINCT V.SID
--                                                    FROM V$MYSTAT V))
-- sys views not visible here
WHERE 1=1
               AND D.ERROR_FLAG = 'N'
-- shoould be NOT NULL; but redundant
--               AND D.LEARNER_ID <> NULL
        HAVING COUNT (D.LEARNER_ID) > 1
      GROUP BY D.LEARNER_ID;

   V_FOUND BOOLEAN := FALSE;
   V_DUPLICATE_IMPORT_IDS   C_DUPLICATE_IMPORT_IDS%ROWTYPE;
BEGIN
   OPEN C_DUPLICATE_IMPORT_IDS;

   LOOP
      FETCH C_DUPLICATE_IMPORT_IDS INTO V_DUPLICATE_IMPORT_IDS;

      EXIT WHEN C_DUPLICATE_IMPORT_IDS%NOTFOUND;

      UPDATE DATA_IMPORT D
         SET D.ERROR_FLAG = 'Y'
       WHERE D.LEARNER_ID = V_DUPLICATE_IMPORT_IDS.LEARNER_ID;

      UPDATE DATA_IMPORT D
         SET D.IMPORT_NOTIFICATION =
                   'DUPLICATE LEARNER_ID IDENTIFIED ('
                || V_DUPLICATE_IMPORT_IDS.LEARNER_ID
                || ').  LEARNER_IDS ERROR_FLAG SET, THIS CASE WILL NOT IMPORT UNTIL CORRECTED.'
       WHERE D.LEARNER_ID = V_DUPLICATE_IMPORT_IDS.LEARNER_ID;

      DBMS_OUTPUT.PUT_LINE (
            'THE FOLLOWING LEARNER WAS IDENTIFIED AS A DUPLICATE '
         || V_DUPLICATE_IMPORT_IDS.LEARNER_ID);

      V_FOUND := TRUE;
   END LOOP;

   CLOSE C_DUPLICATE_IMPORT_IDS;

   IF NOT V_FOUND THEN
      DBMS_OUTPUT.PUT_LINE (
         CHR (10)
         || 'THERE ARE NO DUPLICATE LEARNER_IDS WITHIN THIS UPLOAD.');
   END IF;

   DBMS_OUTPUT.PUT_LINE (CHR (10) || 'STEP 1 COMPLETED');
   COMMIT;
END;
/
1 rows affected

dbms_output:
THE FOLLOWING LEARNER WAS IDENTIFIED AS A DUPLICATE 2

STEP 1 COMPLETED