20
20
21
25
10
21
得如下结果
20 Y
20 N
21 Y
25 Y
10 Y
21 N
------解决方案--------------------
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