The product search returns a list of products using its slug as the
“external key”, because i do not want people seeing the id in links,
and the search product list is just a different rendering of the product
index table.
However, now i had two almost identical select queries for product,
one using the product_id and the other its slug, the former intended for
the form to select products using checkboxes—the one non-JavaScript
users see—and the latter for the product search.
Using the slug in both forms i can now simplify the code and have a
single query.