It's very handy using the CSV importer as demonstrated by Randy Fay, but after the initial import f products I need t keep their stock levels and prices in sync with an external MySQL database at regular intervals.

I've edited this question after successfully having been able to import Taxonomy Terms into my commerce Category Vocabulary using the SQL Feeds Importer - magic! Next - Product and Product References probably via a CSV import although I plan to use the SQL Feeds Importer to update existing Products' stock and price fields.

Not quite sure what went wrong last attempt but in the meantime I had read somewhere that the imported column names had to be in lower case. I'd also read elsewhere that this had been fixed in Drupal 7.14's database interface layer. Anyhow, for good measure, I made sure my SQL request retuned its single column name in lower case; mapped it both to Term Name and Term Description; invoked the standalone form and ..... the imported Taxonomy Terms are happily in my Category Vocabulary.

So I'm confident that I will be able to use the SQL Feeds Importer to keep the Product Price fields up-to-date.

Will report success.