Implicit vs. explicit JOINs

Originally published at https://rivea0.github.io/blog.

Let's say we have a customers table that looks similar to this:

customer_id	first_name	last_name
1	John	Doe
2	Jane	Smith

And an items_ordered table that's looking like this:

customer_id	order_date	item	price
1	2020-01-01	Apple	1.99
2	2020-02-02	Banana	0.99

Usually, we can join them using the INNER JOIN (or just JOIN) clause:

SELECT customer_id, first_name, last_name, order_date, item, price
FROM customers
INNER JOIN items_ordered
ON customers.customer_id = items_ordered.customer_id;

But, there is also another way to do the same thing, which is the implicit JOIN:

SELECT
    customers.customer_id,
    customers.first_name,
    customers.last_name,
    items_ordered.order_date,
    items_ordered.item,
    items_ordered.price
FROM customers, items_ordered
WHERE customers.customer_id = items_ordered.customer_id;

Looks a bit more cluttered.

For clarity's sake, using an explicit JOIN syntax makes more sense, and from what I've read, it seems to be no significant performance difference between the two, and the ANSI 92 standard is said to be recommending using modern explicit joins.