mysql> SELECT * FROM articles;
+----+-----------+
| id | title     |
+----+-----------+
|  1 | Первая    |
|  2 | Вторая    |
|  3 | Третья    |
|  4 | Четвёртая |
+----+-----------+

mysql> SELECT * FROM tags;
+----+---------+
| id | name    |
+----+---------+
|  1 | Метка 1 |
|  2 | Метка 2 |
|  3 | Метка 3 |
|  4 | Метка 4 |
+----+---------+

mysql> SELECT * FROM articles_tags_relations;
+------------+--------+
| article_id | tag_id |
+------------+--------+
|          1 |      2 |
|          1 |      3 |
|          2 |      3 |
|          2 |      4 |
+------------+--------+

+----+-----------+
| id | title     |
+----+-----------+
|  2 | Вторая    |
|  3 | Третья    |
|  4 | Четвёртая |
+----+-----------+

+----+-----------+
| id | title     |
+----+-----------+
|  3 | Третья    |
|  4 | Четвёртая |
+----+-----------+