title: MySQL doesn't use my defined index over a simple select query
body: <p>I've been trying to use an index in my query but to no avail. It's defined, but not used.</p>
  
  <p>Here are my indexes</p>
  
  <pre><code>Table  | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment  
  --------------------------------------------------------------------------------------------------------------------------------------------------------
  alerts |          1 | date_index |            1 | date        | A         |        9825 |     NULL | NULL   |      | BTREE   
  </code></pre>
  
  <p>This my query + explain:</p>
  
  <pre><code>EXPLAIN SELECT latitude, longitude, msg_id
          FROM alerts
          FORCE INDEX(date_index)
          WHERE date&gt;1336312075;
  
  
  | id | select_type | table  | type | possible_keys | key  | key_len | ref  | rows | Extra       |
  --------------------------------------------------------------------------------------------------------
  |  1 | SIMPLE      | alerts | ALL  | date_index    | NULL | NULL    | NULL | 9825 | Using where |
  </code></pre>
  
  <p>The table has 9825 rows, and the date I chose was among the latest 9.... so it should have scanned only 9 rows.</p>
  
  <p>Any ideas? Thanks</p>