I think that you might be able to accomplish this with a special query using the IN keyword with another query like this:
SELECT * FROM articles
WHERE store_name IN (SELECT localStores FROM users where userID = colparam)
colparam defined as:
default value: -1
runtime value: <your userID session variable>
This query should select all from your articles table where the store name is found in a comma separated list of values. This list of values is created with the query that is inside the parenthesis. The query in here is selecting the localstores from your users table for the logged in user. Let me know if you have any further questions on this.