2nd Followup: It turns out that loading a table from a JSON string is more complicated than going from a table to JSON, perhaps for good reason. There does not appear to be a direct inverse to the row_to_json() function, but it wasn't difficult for me to write a PHP program that takes the JSON file I created the other day and converts it back to a series of inserts, recreating the original table.
Of course this simple program does NO validation (not that this file needed any), so if the JSON string is not well-formed for any of a number of reasons, or if it is not properly mapped to the table into which the inserts are made, an insert could fail or result in incorrect data. --
