第一列中按值分组的行总和-T-SQL

Question

I need query that will do the sum of the colB grouped by colA and then multiply with value from colA. After all summing for different groups all sums should be added in total sum. Number of different values in colA could be any.

colA    colB
0.25    100
0.25     80
0.10    200
0.50    160
0.10    500
0.10    150

For given example math should be as follows:

(100+80)*0.25 + (200+500+150)*0.10 + 160*0.50 = 210

Answer 1

If order did matter in this case, you would do something LIKE this:

SELECT SUM(Total) AS GrandTotal
FROM (
SELECT  t.ColA, t.ColA * SUM(t.ColB) AS Total
FROM    dbo.Table1 AS t
GROUP BY t.ColA
    ) AS A

But this should work in this case:

SELECT SUM(ColA * ColB)
FROM dbo.Table1