Question

I have two tables, one showing items users have bought from various stores, and the other which details who bought what.

Table A for products is:

prod_id
site_name
product

Table B for users is:

user_id
prod_id

I need to count the total number of products bought from a certain store. I can’t simply count from Table A as there may be the same products bought by several users but to keep the data tidy I store it as above.

Should I include the site_name in table B going forward as well to make it easier to simply count that, or can it be done in one query? I’d rather not bloat tables for the sake of a couple of queries as I think that would be bad database design but cannot work out how to do the count otherwise.

Is it possible?

Answer 1

You an use a join:

SELECT COUNT(1)
FROM A JOIN B ON A.prod_id = B.prod_id
WHERE A.site_name = 'foo'