SELECT
LEAST(No1, No2) || ':' || GREATEST(No1, No2) AS set_label,
No1,
No2,
SUM(Amount) AS Amount,
Stamp
FROM
tbl
GROUP BY
GROUPING SETS (
(LEAST(No1, No2), GREATEST(No1, No2), No1, No2, Stamp),
(LEAST(No1, No2), GREATEST(No1, No2))
)
http://sqlfiddle.com/#!4/9afd5/18
Skulle vara bättre om varje rad har en unik identifierare...
http://sqlfiddle.com/#!4/e9e95/1