saya mau tanya mengenai LEFT JOIN,
ini ada tabel shop, kolomnya:
article
dealer
price

isi tabelnya:

+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | A | 3.45 |
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | B | 1.45 |
| 0003 | C | 1.69 |
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+

pertanyaan:
Task: Find the number, dealer, and price of the most expensive article.

jawaban:
SELECT s1.article, s1.dealer, s1.price
FROM shop s1
LEFT JOIN shop s2 ON s1.price < s2.price
WHERE s2.article IS NULL;

hasil:
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0004 | D | 19.95 |
+---------+--------+-------+

saya mau menanyakan untuk left joinnya ,maksud s1.price < s2.price (ngga nge, soalnya yg sering s1.price = s2.price) ??,kemudian di kriteria where s2.article IS NULL maksudnya apa??

mohon pencerannya dari agan2 yang jago query
trims.......