Question

I have a categories table which lists about 35 possible categories. I then also have an Item table where one of the foreign keys relates back to a category in the categories table. On my index page I’m looking to just show how many items are in each category. I’m just unsure what the best way to go about this is, in terms of building a more efficient query and reducing the number of calls to the DB.

Any thoughts would be great

Thanks

Answer 1

You are looking for a simple aggregation query:

select c.categoryName, count(i.itemId) as NumItems
from category c left outer join
     items i
     on c.categoryID = i.categoryID
group by c.categoryName
order by NumItems desc

The left outer join gets all categories, even if they do not have any items.