ms access compare value with average of trailing seven days - sql

Question

I have a data set which contains people, dates, food, and quantity of food. I want a query where I specify a person and a date and have two values returned: the quantity of food eaten on the date chosen and the average quantity of food eaten over the previous 7 days.
So if I pick Abe on 1/10/2013 I get "1" and "3.6" because he ate 1 piece of fruit on 1/10 and an average of 3.6 pieces of fruit each day between 1/3 and 1/9.
name,thedate,qty,food
name,thedate,qty,food
abe,1/2/2013,1,orange
abe,1/2/2013,3,pear
abe,1/3/2013,3,orange
abe,1/4/2013,2,orange
abe,1/4/2013,2,plum
abe,1/5/2013,1,orange
abe,1/7/2013,7,onion
abe,1/8/2013,2,orange
abe,1/9/2013,3,orange
abe,1/9/2013,2,pear
abe,1/10/2013,1,orange
jen,1/1/2013,2,orange
jen,1/4/2013,3,orange
jen,1/5/2013,2,orange

Answer 1

You need a correlated subquery to find this
Select
Parent.name
, Parent.thedate
, Parent.qty,
(SELECT avg(qty)
FROM yourTable
where name = parent.name
and thedate < parent.theDate
and theDate>=dateadd("d", datediff("d",0, parent.theDate)-7,0)
group by name) as previousSeven
from yourTable Parent
If this is actually on a per fruit-type basis you can join on that too with and fruit = parent.fruit you need to add fruit to the group by, too
Update
To find, not an average, but the sum of the number of fruit divided by the number of distinct days with data in the last 7 days you will need something more like this (it get's a lot more complicated because access doesn't support the Select count(distinct something) syntax)
Select
Name
, theDate
, qty
, sumOfPreviousSeven/distinctDaysWithDataLastSeven
from (
Select
Parent.name
, Parent.thedate
, Parent.qty
, (SELECT sum(qty)
FROM table4
where name = parent.name
and thedate < parent.theDate
and theDate>=dateadd("d", datediff("d",0, parent.theDate)-7,0)
group by name) as sumOfPreviousSeven
, (select top 1 count(distinctDates) from
(select dateadd("d", datediff("d",0, theDate),0) as distinctDates, name from table4
group by dateadd("d", datediff("d",0, theDate),0), name)
where name = parent.name
and distinctDates < parent.theDate
and distinctDates>=dateadd("d", datediff("d",0, parent.theDate)-7,0)
group by name) as distinctDaysWithDataLastSeven
from table4 Parent) as base