SELECT newprice list.PartNumber
FROM newprice list
LEFT JOIN `price list` ON newprice list.PartNumber = price list.PartNumber
WHERE price list.PartNumber IS NULL
If you are going to have table names with spaces in them then you will need to put backticks around the name (e.g. `price list`). I would recommend renaming the tables and changing the spaces to underscores.