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SELECT COL1,COL2 FROM
(SELECT T.*,ROW_NUMBER() OVER(PARTITION BY COL1 ORDER BY DBMS_RANDOM.VALUE) RN FROM T )
WHERE RN<=2
SELECT COL1,COL2 FROM
(SELECT T.*,ROW_NUMBER() OVER(PARTITION BY COL1 ORDER BY COL2) RN FROM T )
WHERE RN<=2