SQL：要約された値で行を挿入します

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

各行に一意の識別子があるとよいでしょう...

http://sqlfiddle.com/#!4/e9e95/1