Så här:
;WITH cte
AS
(
SELECT ColumnB, SUM(ColumnA) asum
FROM @t
gROUP BY ColumnB
), cteRanked AS
(
SELECT asum, ColumnB, ROW_NUMBER() OVER(ORDER BY ColumnB) rownum
FROM cte
)
SELECT (SELECT SUM(asum) FROM cteRanked c2 WHERE c2.rownum <= c1.rownum),
ColumnB
FROM cteRanked c1;
Detta bör ge dig:
ColumnA ColumnB
3 a
6 b
10 c
15 d