Sorting inventory by date

[BJ9]

I'm new to writing reports in PostegrSQL. Any help will be greatly appreciated.

All our inventory is entered into the database with a date_in and cost fields. I'm trying to pull this data out sorting it by category then summing it by date group (i.e., 0-90 days) within each category.

The report runs fine with just the totals by category (before I try to break it out by date). I can't seem to figure out the right way to break the totals out into the date groups I want.

This is my code so far.

select store.short_name || ' (' || store.store_id || ')' as \"Store\", 
inventory.description as \"Description\", 
category_number as \"Category\",
sum (cost) as \"Total\",
  (select inventory.cost,
    CASE 
       when inventory.date_in between today and today - ('90 days') then sum end as \"0-90 Days\"
	when inventory.date_in between today - ('91 days') and today - ('120 days') then sum end as \"91-120 Days\"
	when inventory.date_in between today - ('121 days') and today - ('180 days') then sum end as \"121-180 Days\"
	when inventory.date_in between today - ('181 days') and today - ('240 days') then sum end as \"181-240 Days\"
	else inventory.date_in between today - ('241 days') and today -('infinity') then sum end as \"240+ Days\"
		)
	from store
join inventory on store.store_id = inventory.store_id
where store.store_id in $stores
group by store.short_name, store.store_id, inventory.description, store.sort_id, inventory.category_number
	order by sort_id,category_number

I've got the feeling I'm missing something very simple in how I'm writing this. Can anyone point me in the right direction.

Thanks