WITH ta AS (SELECT 20 a FROM dual UNION ALL SELECT 20 a FROM dual UNION ALL SELECT 21 a FROM dual UNION ALL SELECT 25 a FROM dual UNION ALL SELECT 10 a FROM dual UNION ALL SELECT 21 a FROM dual )SELECT A, DECODE(ROW_NUMBER() OVER(PARTITION BY A ORDER BY ROWNUM), 1, 'Y', 'N') FROM TA ORDER BY ROWNUM
WITH ta AS
(SELECT 20 a FROM dual UNION ALL
SELECT 20 a FROM dual UNION ALL
SELECT 21 a FROM dual UNION ALL
SELECT 25 a FROM dual UNION ALL
SELECT 10 a FROM dual UNION ALL
SELECT 21 a FROM dual
)SELECT A,
DECODE(ROW_NUMBER() OVER(PARTITION BY A ORDER BY ROWNUM),
1,
'Y',
'N')
FROM TA
ORDER BY ROWNUM