Oracle 11g Release 2

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CREATE TABLE table_name (S_No, A_Port, B_port) AS
SELECT 1,  80, 100 FROM DUAL UNION ALL
SELECT 2,  90, 110 FROM DUAL UNION ALL
SELECT 3, 100,  80 FROM DUAL UNION ALL
SELECT 4,  94, 106 FROM DUAL;
4 rows affected

MERGE INTO table_name dst
USING (
  SELECT ROWID rid,
         ROW_NUMBER() OVER (
           PARTITION BY LEAST(A_Port, B_Port), GREATEST(A_Port, B_Port)
           ORDER BY S_no
         ) AS rn
  FROM   table_name
) src
ON (dst.ROWID = src.rid AND src.rn > 1)
WHEN MATCHED THEN
  UPDATE SET A_port = NULL
  DELETE WHERE 1 = 1;
1 rows affected

SELECT * FROM table_name;


S_NO
A_PORT
B_PORT


1
80
100

2
90
110

4
94
106