SUM of clumps of different items sold

Guys and Gals,
Please be so kind and help with a formula for the following dillemma:

I have a 7000 row spreadsheet of items sold over the past 6 months. I sorted them by their SKU, but some of them sold in multiple qty in a given day.

What is a formula to calculate the total qty of each SKU sold?

Example:
Column A = SKU 001
Column B = Qty Sold in a particular purchase (most have 1, but some are 2 or 3 or 4, etc.)
Column C, (Row 10) = Total where I would like to come up with a number for columns 1-10 (for example).

next item:
Column A = SKU 002
Column B = Qty Sold in a particular purchase (most have 1, but some are 2 or 3 or 4, etc.)
Column C, (Row 17) = Total where I would like to come up with a number for columns 11-17 (for example).

P.S. Rows per SKU vary (they represent each purchase of a given item)

THANK YOU INFINITELY IN ADVANCE FOR A SOLUTION

Can you upload an example of that spreadsheet? Are all 3 columns (A,B,C) in all rows? Do you have multiple listings of SKU numbers?

Lets' say your SKU start in C2 and your QTY in D2, In E2 try

=IF(B1<>B2,SUMPRODUCT(--($C$2:$C$8000=C2),($D$2:$D$8000)),"")

Dragged down. Does that work for you?

Okay, this assumes you have sorted your SKU #'s. In AD2 and dragged down

=IF(AB2<>AB3,SUMPRODUCT(--($AB$2:$AB$8000=AB2),($AC$2:$AC$8000)),"")

Does that work?