Oracle 23c

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create table ISOLATION_AREA_ASSETS (
  G3E_FID number,
  UPSTREAM_ISO_FID number,
  DOWNSTREAM_ISO_FIDS number
)
create PROCEDURE TRAVERSE_TRACE(
                            G3E_FID IN NUMBER
                        ) IS
                            
    v_G3E_FID NUMBER := G3E_FID;
    v_downstreamIsolators VARCHAR2(2048);
    v_row_count NUMBER;
    
BEGIN
    dbms_output.enable(null);
           
    Insert Into ISOLATION_AREA_ASSETS (G3E_FID, UPSTREAM_ISO_FID, DOWNSTREAM_ISO_FIDS)
    VALUES (16312200, 16309677, null);
 
    Insert Into ISOLATION_AREA_ASSETS (G3E_FID, UPSTREAM_ISO_FID, DOWNSTREAM_ISO_FIDS)
    VALUES (16309676, 16309677, null);

    v_downstreamIsolators := '16312200';

    SELECT COUNT(*)
    INTO v_row_count
    FROM ISOLATION_AREA_ASSETS
    WHERE UPSTREAM_ISO_FID = TRAVERSE_TRACE.G3E_FID;
    DBMS_OUTPUT.PUT_LINE('Number of rows where UPSTREAM_ISO_FID = ' || G3E_FID || ' is: ' || v_row_count);
            
    DBMS_OUTPUT.PUT_LINE('Updating DOWNSTREAM_ISO_FIDS to ' || v_downstreamIsolators || ' where upstream ISO FID = ' || G3E_FID);
    UPDATE ISOLATION_AREA_ASSETS
    SET DOWNSTREAM_ISO_FIDS = to_char(v_downstreamIsolators)
    WHERE UPSTREAM_ISO_FID = TRAVERSE_TRACE.G3E_FID;
    DBMS_OUTPUT.PUT_LINE('Number of rows updated = ' || SQL%ROWCOUNT);
END TRAVERSE_TRACE;
/
select * from user_errors
begin
    dbms_output.enable;
    TRAVERSE_TRACE(16309677);
end;
/
1 rows affected

dbms_output:
Number of rows where UPSTREAM_ISO_FID = 16309677 is: 2
Updating DOWNSTREAM_ISO_FIDS to 16312200 where upstream ISO FID = 16309677
Number of rows updated = 2

select * from ISOLATION_AREA_ASSETS;


G3E_FID
UPSTREAM_ISO_FID
DOWNSTREAM_ISO_FIDS


16312200
16309677
16312200

16309676
16309677
16312200