emdin

"The duplicate 'Alice' is not an intended behavior. The description would be accurate if it stated, 'All rows from the left table, and some rows may appear several times, depending on the specific table configuration.'

I hope you see that we are discussing semantics here. There are no mistakes in the article, and I'm unsure why it sparked such a debate. I've often seen juniors confused by JOIN behavior, and this article provides some good mental models to help avoid similar pitfalls.

So you suggest ON condition would work as described in examples even if id is not primary key and not a unique index?

Lets build an example.

CREATE TABLE tbl_a (id INT PRIMARY KEY, name VARCHAR(255));

CREATE TABLE tbl_b (id INT, name VARCHAR(255));
INSERT INTO tbl_a (id, name) VALUES (1, 'Alice');
INSERT INTO tbl_a (id, name) VALUES (2, 'Bob');
INSERT INTO tbl_a (id, name) VALUES (3, 'Charlie');
INSERT INTO tbl_b (id, name) VALUES (1, 'Delta');
INSERT INTO tbl_b (id, name) VALUES (1, 'Echo');
INSERT INTO tbl_b (id, name) VALUES (2, 'Foxtrot');

SELECT tbl_a.name as name FROM tbl_a LEFT JOIN tbl_b ON tbl_a.id = tbl_b.id

Last JOIN will yield Alice twice, which definitely not a "All rows from the left table".

I would prefer to discuss the specific aspects of the article you found incorrect, rather than engaging in a sarcasm battle.