Create column containing average value for product and deviation for each row

[jmkvalsund]

Hi,

I have a table containing productcode and achieved price for each sale (row).

Now I want to calculate the difference from the average sale for the actual product on each row, like this:

Product	Achieved price	Diff from average price
A	50	-8,333
A	60	1,666
A	65	6,666
B	187	-2,500
B	192	2,500
C

And there are about 30000 sales and 50 products in the current table.
I've tried some combinations of AVERAGE (would prefer MEDIAN though) but I just don't get how to filter on products...

Anyone?

Regards,

John