mysql> explain select node, content.version from metadata,content where metadata_type="category" and metadata_value="Restaurants" and metadata.node=content.name and metadata.version=content.version;
+----+-------------+----------+-------+-----------------------------------------+----------------+---------+------------------------------------------------------+-------+-------------+
| id | select_type | table    | type  | possible_keys                           | key            | key_len | ref                                                  | rows  | Extra       |
+----+-------------+----------+-------+-----------------------------------------+----------------+---------+------------------------------------------------------+-------+-------------+
| 1  | SIMPLE      | content  | index | PRIMARY                                 | PRIMARY        | 204     |                                                      | 16446 | Using index |
| 1  | SIMPLE      | metadata | ref   | metadata_index,version,node,metadata_vn | metadata_index | 408     | ogboston.content.name,ogboston.content.version,const | 1     | Using where |
+----+-------------+----------+-------+-----------------------------------------+----------------+---------+------------------------------------------------------+-------+-------------+
2 rows in set (0.00 sec)

mysql> create index metadata_tv on metadata (metadata_type, metadata_value(10));                                                                                       Query OK, 370114 rows affected (22.74 sec)
Records: 370114  Duplicates: 0  Warnings: 0

mysql> explain select node, content.version from metadata,content where metadata_type="category" and metadata_value="Restaurants" and metadata.node=content.name and metadata.version=content.version;
+----+-------------+----------+--------+-----------------------------------------------------+-------------+---------+--------------------------------------------------+------+--------------------------+
| id | select_type | table    | type   | possible_keys                                       | key         | key_len | ref                                              | rows | Extra                    |
+----+-------------+----------+--------+-----------------------------------------------------+-------------+---------+--------------------------------------------------+------+--------------------------+
| 1  | SIMPLE      | metadata | range  | metadata_index,version,node,metadata_vn,metadata_tv | metadata_tv | 214     |                                                  | 2242 | Using where              |
| 1  | SIMPLE      | content  | eq_ref | PRIMARY                                             | PRIMARY     | 204     | ogboston.metadata.node,ogboston.metadata.version | 1    | Using where; Using index |
+----+-------------+----------+--------+-----------------------------------------------------+-------------+---------+--------------------------------------------------+------+--------------------------+
2 rows in set (0.00 sec)