combine groupby with sum

hi,

I could realy use your help on this one 🙂

I have two tables, both containing a key wich i could use to match rows of the two tables.

But, this would be a many to many realtion because in both table the key is present more than 1 time.

what i to compute is the total sales amount by key from table A, and then also compute the total sales amount by key of table B.

for table A i have used groupby. But now i would like to add a column in which the sum of sales by key from table B is shown. That way i can compare "Amount_By_Key" with "SAM sum of sales" per "key".

Basically i want to compare the total sales amount by key in table A with table B. 

NOTE: some keys that excist in table A dont appear in table B. 

please find attached the data: OneDrive data