>> Note: I don't know what SKU is, but if this is a quantity, you can sum it too or something like that <<

SKU = Stock Keeping Unit. It might also be called an item or a product. Examples: Kellogg's Corn Flakes 20 ounce, "Abbey Road" CD by The Beatles, Panasonic 27 inch color TV Model XYZ, etc. Although SKUs are often numeric, you wouldn't perform any arithmetic operations on them.

Mike