Question

what is the different between this queries? which one should I prefer and why?

SELECT
t1.*,
t2.x
FROM
t1,
t2
WHERE
t2.`id` = t1.`id`

or

SELECT
t1.*,
t2.x
FROM
t1
INNER JOIN                                                  # LEFT JOIN ?
t2
ON t2.`id` = t1.`id`

Does using commas has the same effect than use LEFT JOINS?

That’s embarrassing. It’s the first time I asked myself about this for years. I ever used the first version, but now i’m feeling like I missed some lines in my first SQL induction. 😉

Answer 1

The “comma” syntax is equivalent to the INNER JOIN syntax. The query optimizer should be running the same query for you regardless of how you ask for it. There’s a general recommendation to do your joins using the JOIN language and do your filtering using the WHERE language as it makes your intention more clear