I have the following 2 datasets, each describing a catalogue of items: the item's part number, price and verbal description. The left dataset is the out-of-date catalogue and the right one is the up-to-date catalogue.

Note that it is possible that there are items in the new catalogue that are not present in the old one, as happens with "spanner".

Question: How can I create a new data set with the prices updated?

Data is

old = Dataset[{
    <|"part nu" -> "045", "price" -> 8.9, "description" -> "cutter"|>,
    <|"part nu" -> "014", "price" -> 9.3, "description" -> "plier"|>,
    <|"part nu" -> "106", "price" -> 4.6, "description" -> "pipe wrench"|>,
    <|"part nu" -> "183", "price" -> 24.1, "description" -> "screwdriver"|>,
    <|"part nu" -> "283", "price" -> 0.8, "description" -> "washer"|>
   }]

new = Dataset[{
    <|"part nu" -> "045", "price" -> 9.2, "description" -> "cutter"|>,
    <|"part nu" -> "014", "price" -> 9.5, "description" -> "plier"|>,
    <|"part nu" -> "612", "price" -> 10.9, "description" -> "spanner"|>,
    <|"part nu" -> "106", "price" -> 4.2, "description" -> "pipe wrench"|>,
    <|"part nu" -> "183", "price" -> 24., "description" -> "screwdriver"|>,
    <|"part nu" -> "283", "price" -> 0.8, "description" -> "washer"|>
  }]