SELECT 'A' GBN, 1 RN FROM DUAL UNION ALL
SELECT '', 2 FROM DUAL UNION ALL
SELECT '', 3 FROM DUAL UNION ALL
SELECT 'B', 4 FROM DUAL UNION ALL
SELECT '', 5 FROM DUAL UNION ALL
SELECT 'C', 6 FROM DUAL UNION ALL
SELECT '', 7 FROM DUAL UNION ALL
SELECT '', 8 FROM DUAL UNION ALL
SELECT '', 9 FROM DUAL UNION ALL
SELECT '', 10 FROM DUAL UNION ALL
SELECT '', 11 FROM DUAL UNION ALL
SELECT '', 12 FROM DUAL UNION ALL