I am trying to learn subquery and I can't wrap my head around this one and hoping someone can show me.

Say table [tbl_Info] has these fields:
1. Week
2. Item
3. Store Number
4. Sales

How should I write a subquery to count the number of stores the have 0 sales for each particular item?

You haven't posted enough information to answer that question. Please post the whole assignment so we can see what the intructor is trying to teach and the other information needed to solve this problem.

-PatP

PatP, thanks for your reply. Do you understand the question? What else do you need to answer to suggest a solution?

Side note, I am the instructor teaching myself SQL.

You have to determine all stores and subtract all stores that do have some sales. The EXCEPT operator or a NOT EXISTS predicate would be a good start.

For the moment, let's not worry about the subquery. The first thing you need to do is determine the number of sales per store per item. This should be a relatively straightforward query, and we can use this in your final query.