Set up a table of categories with one record for each category.
Not only can this be used to produce your portal, this table can serve as the source of values for a value list of your categories.
Thanks for the response, PhilModJunk. I considered that. Except I have more than just one Category field; each Category has Subcategories, and some of those have SubSubCategories. If I have a separate tables for Categories, Subcategories, etc., it now becomes a project to maintain them all.
Is this my only option?
That seems like all the more reason not to try to manage this data in the products table
Depending on what you need to do with this data, there may be other options, but I don't have much to go on from what you have described thus far.
ExecuteSQL, for example, can list Distinct values in a single field that might be formatted to look and function much like a portal as long as you don't have to edit data in that portal.
And I've been able to gin up filtered portals that drop out all but the first instance of each value in a given field. But I'd not try that from the products table, I'd set up a table to manage the categories and the sub categories and use the filter to drop out duplicates in a portal to that much smaller number of records.
How will you use this portal of categories once you have it up on your layout?