How to calculate Sales of previous weeks

[nguyenviethung]

Hi everyone,

I got data like this:

Date	Product	Sales
4/28/2018	A	1
4/29/2018	A	2
4/30/2018	A	3
5/1/2018	A	4
5/2/2018	A	5
5/3/2018	A	6
5/4/2018	A	7
5/5/2018	A	8
5/6/2018	A	9
5/7/2018	A	10
5/8/2018	A	11
5/9/2018	A	12
5/10/2018	A	13
5/11/2018	A	14
5/12/2018	A	15
5/13/2018	A	16
5/14/2018	A	17
5/15/2018	A	18
5/16/2018	A	19
5/17/2018	A	20
5/18/2018	A	21

Date will be loaded with AutoCalendar function in Qlik Sense and bear Date.autoCalendar.Week.

Now what i want is a table of calulation like this:

Week	Sales (expression -> result)	Previous-Week-Sales
W17	=Sum(Sales) -> 1	??? ->  -
W18	=Sum(Sales) -> 35	??? -> 1
W19	=Sum(Sales) -> 84	??? -> 35
W20	=Sum(Sales) -> 111	??? -> 84

Can anyone help me the expression to calculate the previous-week-sales for each week like this? Thank you all of you.

[MK_QSL · Accepted solution]

SUM(Sales)

&

Above(SUM(Sales))

[nguyenviethung]

Thank you. Love you..