title: optimize mysql count query
body: <p>Is there a way to optimize this further or should I just be satisfied that it takes 9 seconds to count 11M rows ?</p>
  <pre><code>devuser@xcmst &gt; mysql --user=user --password=pass -D marctoxctransformation -e &quot;desc record_updates&quot;                                                                    
  +--------------+----------+------+-----+---------+-------+
  | Field        | Type     | Null | Key | Default | Extra |
  +--------------+----------+------+-----+---------+-------+
  | record_id    | int(11)  | YES  | MUL | NULL    |       | 
  | date_updated | datetime | YES  | MUL | NULL    |       | 
  +--------------+----------+------+-----+---------+-------+
  devuser@xcmst &gt; date; mysql --user=user --password=pass -D marctoxctransformation -e &quot;select count(*) from record_updates where date_updated &gt; '2009-10-11 15:33:22' &quot;; date                         
  Thu Dec  9 11:13:17 EST 2010
  +----------+
  | count(*) |
  +----------+
  | 11772117 | 
  +----------+
  Thu Dec  9 11:13:26 EST 2010
  devuser@xcmst &gt; mysql --user=user --password=pass -D marctoxctransformation -e &quot;explain select count(*) from record_updates where date_updated &gt; '2009-10-11 15:33:22' &quot;      
  +----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
  | id | select_type | table          | type  | possible_keys                                          | key                                                    | key_len | ref  | rows     | Extra                    |
  +----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
  |  1 | SIMPLE      | record_updates | index | idx_marctoxctransformation_record_updates_date_updated | idx_marctoxctransformation_record_updates_date_updated | 9       | NULL | 11772117 | Using where; Using index | 
  +----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
  devuser@xcmst &gt; mysql --user=user --password=pass -D marctoxctransformation -e &quot;show keys from record_updates&quot;
  +----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+
  | Table          | Non_unique | Key_name                                               | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
  +----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+
  | record_updates |          1 | idx_marctoxctransformation_record_updates_date_updated |            1 | date_updated | A         |        2416 |     NULL | NULL   | YES  | BTREE      |         | 
  | record_updates |          1 | idx_marctoxctransformation_record_updates_record_id    |            1 | record_id    | A         |    11772117 |     NULL | NULL   | YES  | BTREE      |         | 
  +----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+
  </code></pre>