SELECT Date, Discount,
dense_rank() OVER (partition by Discount order by Date) AS RankValue FROM (
SELECT '2021-10-01 15:54:58' AS 'Date', 17 'Discount' UNION ALL
SELECT '2021-10-01 15:55:58', 17 UNION ALL
SELECT '2021-10-01 15:56:58', 17 UNION ALL
SELECT '2021-10-01 16:57:58', 17 UNION ALL
SELECT '2021-10-01 15:58:58', 18 UNION ALL
SELECT '2021-10-01 15:59:58', 17 ) t