gistfile1.txt

mysql> explain select s.branch_name 
from build_state s 
where s.branch_name is not null 
and s.id in (select h.build_state_id from history h where h.build_type_id = 'bt400' and h.build_start_time_server > 1353004041189);

+----+--------------------+-------+----------------+-------------------------------------------------------+------------------+---------+------+-------+-------------+
| id | select_type        | table | type           | possible_keys                                         | key              | key_len | ref  | rows  | Extra       |
+----+--------------------+-------+----------------+-------------------------------------------------------+------------------+---------+------+-------+-------------+
|  1 | PRIMARY            | s     | ALL            | NULL                                                  | NULL             | NULL    | NULL | 47559 | Using where |
|  2 | DEPENDENT SUBQUERY | h     | index_subquery | start_time_index,build_type_id_index,history_state_id | history_state_id | 9       | func |     1 | Using where |
+----+--------------------+-------+----------------+-------------------------------------------------------+------------------+---------+------+-------+-------------+
2 rows in set (0.00 sec)