I deleted the product attribute "category_id" from the default product attribute set because I added it to the default product attribute set when trying to resolve a problem.. but when I re-index it returned an error and all the products were missing from the Front end.
But now I can't select a product category when adding or editing products. The category selector is not there.
I now understand the importance of the category_id attribute.
Can I simple re-insert the attribute back into eav_attribute table or are there other tables to consider?