USING in the JOIN

mysql> SELECT id FROM t1;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
+----+
mysql> SELECT id FROM t2;
+----+
| id |
+----+
|  2 |
|  3 |
|  4 |
+----+
mysql> SELECT id FROM t1 LEFT JOIN t2 USING(id);