test.txt

Table users:
+----+---------+
| id |  name   |
+----+---------+
|  1 | Mathieu |
|  2 | Ynk     |
+----+---------+

Table articles:

+----+-----------+-------------------+
| id | user_id |       title       |
+----+-----------+-------------------+
|  1 |         1 | Mon super article |
+----+-----------+-------------------+


SELECT * FROM users INNER JOIN articles ON articles.user_id = users.id

+---------+-----------+------------+-------------------+-------------------+
| user.id | user.name | article.id | article.user_id   |   article.title   |
+---------+-----------+------------+-------------------+-------------------+
|       1 | Mathieu   | 1          | 1                 | Mon super article |
+---------+-----------+------------+-------------------+-------------------+

SELECT * FROM users LEFT JOIN articles ON articles.user_id = users.id

+---------+-----------+------------+-------------------+-------------------+
| user.id | user.name | article.id | article.user_id   |   article.title   |
+---------+-----------+------------+-------------------+-------------------+
|       1 | Mathieu   | 1          | 1                 | Mon super article |
|       2 | Ynk       | null       | null              | null              |
+---------+-----------+------------+-------------------+-------------------+