Personal Catalogue: PHP & MySQL — Chapter 6, Exercise 2
====================================================

TASK
Search with an empty search term but the type dropdown set to "cd."
Explain, using the SQL your own PHP would build for this case, why
every CD in the catalogue is returned even though the search box was
left blank.

SOLUTION

With the search box empty and the type dropdown set to "cd" (assuming
item_type_id 2, per the item_types seed data from Chapter 1), the URL
is:

    search.php?q=&type=2&tag=0

$searchTerm ends up as '' (an empty string, after trim()). The PHP
still builds:

    SELECT items.* FROM items
    WHERE (items.title LIKE :query OR items.creator LIKE :query)
    AND items.item_type_id = :type_id
    ORDER BY items.title

    params: ['query' => '%%', 'type_id' => 2]

The key detail: $params['query'] is '%' . '' . '%', which evaluates to
just '%' — the wildcard character on its own, with nothing between the
two percent signs. In SQL's LIKE syntax, a bare '%' pattern means
"match any sequence of characters, including zero characters" — so
LIKE '%' matches every single row's own title (and every creator),
regardless of what's actually in that column, including NULL-free
empty strings.

Since every CD's title genuinely matches LIKE '%', and the AND
items.item_type_id = :type_id clause still correctly narrows the
result down to only item_type_id = 2, the combined effect is: every
row where LIKE '%' is true (all of them) AND item_type_id = 2 is true
— which is exactly every CD in the catalogue.

Confirm at the mysql> prompt:

    SELECT title FROM items WHERE title LIKE '%' AND item_type_id = 2;

Expected output: every real CD title currently in the catalogue.

WHY THIS WORKS AS AN ANSWER
----------------------------
It correctly identifies the specific mechanism (an empty search term
collapses to the bare wildcard '%', which matches everything) rather
than just observing that "it works," and confirms the type filter
still narrows the otherwise-match-everything query down correctly.