mysql> explain SELECT username, picture FROM friends INNER JOIN members ON members.id = '9470' WHERE picture != 'NULL';
+----+-------------+---------+-------+---------------+---------+---------+-------+-------+-------------+
| id | select_type | table   | type  | possible_keys | key     | key_len | ref   | rows  | Extra       |
+----+-------------+---------+-------+---------------+---------+---------+-------+-------+-------------+
|  1 | SIMPLE      | members | const | PRIMARY       | PRIMARY | 3       | const |     1 |             | 
|  1 | SIMPLE      | friends | index | NULL          | PRIMARY | 3       | NULL  | 30155 | Using index | 
+----+-------------+---------+-------+---------------+---------+---------+-------+-------+-------------+