mysql> explain SELECT type,email FROM lists join (aliases) on (aliases.uid=lists.uid) WHERE lists.uid = 'etbe@example.com' or aliases.alias='etbe@example.com';                                                                                                                                                                   
+----+-------------+---------+-------+------------------------------------+------------+---------+-------------------+----------+--------------------------+                                                                                                                                                                                                 
| id | select_type | table   | type  | possible_keys                      | key        | key_len | ref               | rows     | Extra                    |                                                                                                                                                                                                 
+----+-------------+---------+-------+------------------------------------+------------+---------+-------------------+----------+--------------------------+                                                                                                                                                                                                 
|  1 | SIMPLE      | lists   | index | lists_index_constraint,lists_index | lists_type |       1 | NULL              | 18473452 | Using index              |                                                                                                                                                                                                 
|  1 | SIMPLE      | aliases | ref   | idx_alias,idx_uid                  | idx_uid    |     255 | example.lists.uid |        1 | Using where; Using index |                                                                                                                                                                                                 
+----+-------------+---------+-------+------------------------------------+------------+---------+-------------------+----------+--------------------------+                                                                                                                                                                                                 
2 rows in set (0.00 sec)                                                                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                                                                                
mysql> explain SELECT type,email FROM lists WHERE uid = 'etbe@example.com';                                                                                                                                      
+----+-------------+-------+------+------------------------------------+-------------+---------+-------+------+--------------------------+                                                                                                                                                                                                                      
| id | select_type | table | type | possible_keys                      | key         | key_len | ref   | rows | Extra                    |                                                                                                                                                                                                                      
+----+-------------+-------+------+------------------------------------+-------------+---------+-------+------+--------------------------+                                                                                                                                                                                                                      
|  1 | SIMPLE      | lists | ref  | lists_index_constraint,lists_index | lists_index |     255 | const |  115 | Using where; Using index |                                                                                                                                                                                                                      
+----+-------------+-------+------+------------------------------------+-------------+---------+-------+------+--------------------------+                                                                                                                                                                                                                      
1 row in set (0.00 sec)
mysql> explain SELECT type,email FROM lists right join (aliases) on (aliases.uid=lists.uid) WHERE lists.uid = 'etbe@example.com' or aliases.alias='etbe@example.com';
+----+-------------+---------+-------+------------------------------------+-------------+---------+---------------------+---------+--------------------------+
| id | select_type | table   | type  | possible_keys                      | key         | key_len | ref                 | rows    | Extra                    |
+----+-------------+---------+-------+------------------------------------+-------------+---------+---------------------+---------+--------------------------+
|  1 | SIMPLE      | aliases | index | idx_alias                          | idx_uid     |     255 | NULL                |    2073 | Using index              |
|  1 | SIMPLE      | lists   | ref   | lists_index_constraint,lists_index | lists_index |     255 | example.aliases.uid | 1026180 | Using where; Using index |
+----+-------------+---------+-------+------------------------------------+-------------+---------+---------------------+---------+--------------------------+
2 rows in set (0.00 sec)