Personal Catalogue: PHP & MySQL — Chapter 3, Exercise 1
====================================================

TASK
Wire up add_item.php against the real catalogue database and add three
items: one book, one CD, and one DVD. Confirm all three appear
correctly with SELECT * FROM items;, including that each row's unused
columns (e.g. a DVD's own creator) are stored as NULL, not an empty
string.

SOLUTION

With config.php, functions.php, and add_item.php in place and pointed
at the real catalogue database, visiting add_item.php in a browser and
submitting the form three times with:

    Type: book
    Title: Fluent Python
    Creator: Luciano Ramalho
    Format detail: paperback
    Release year: 2022
    Notes: (left blank)

    Type: cd
    Title: The Dark Side of the Moon
    Creator: Pink Floyd
    Format detail: album
    Release year: 1973
    Notes: (left blank)

    Type: dvd
    Title: The Matrix
    Creator: (left blank)
    Format detail: (left blank)
    Release year: 1999
    Notes: (left blank)

Then, at the mysql> prompt:

    SELECT * FROM items;

Expected output (id/created_at values will differ):

    +----+--------------+----------------------------+-------------------+----------------+--------------+-------+
    | id | item_type_id | title                      | creator            | format_detail  | release_year | notes |
    +----+--------------+----------------------------+-------------------+----------------+--------------+-------+
    |  1 |            1 | Fluent Python               | Luciano Ramalho    | paperback      |         2022 | NULL  |
    |  2 |            2 | The Dark Side of the Moon   | Pink Floyd         | album          |         1973 | NULL  |
    |  3 |            3 | The Matrix                  | NULL               | NULL           |         1999 | NULL  |
    +----+--------------+----------------------------+-------------------+----------------+--------------+-------+

Confirming NULL rather than empty string specifically:

    SELECT title, creator IS NULL AS creator_is_null
    FROM items
    WHERE title = 'The Matrix';

Expected: creator_is_null returns 1 (true) — the column genuinely
holds NULL, not an empty '' value.

WHY THIS WORKS AS AN ANSWER
----------------------------
It actually exercises all three real item types through the live form
rather than only inserting rows by hand, and specifically verifies the
NULL-vs-empty-string distinction with an IS NULL check rather than
just eyeballing the output, since a blank-looking cell in a terminal
can't always be trusted to distinguish the two.