title: MySQL not using index when checking = 1 , but using it with = 0
body: <p>Here is a perplexing issue I am having:</p>
  
  <pre><code>Query:
  EXPLAIN SELECT id,hostname FROM queue_servers WHERE live=1
  
  id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
  
  1   SIMPLE  queue_servers   ALL     live    NULL    NULL    NULL    6   Using where
  </code></pre>
  
  <hr>
  
  <pre><code>Query:
  EXPLAIN SELECT id,hostname FROM queue_servers WHERE live=0
  
  id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
  
  1   SIMPLE  queue_servers   ref     live    live    1   const   1
  </code></pre>
  
  <hr>
  
  <pre><code>SHOW INDEXES FROM queue_servers
  
  Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type
  
  queue_servers   1   live    1   live    A   6   NULL    NULL        BTREE
  </code></pre>
  
  <hr>
  
  <p>Any ideas? This is making me go crazy.. If I just try selecting a single column like this:</p>
  
  <pre><code>EXPLAIN SELECT id FROM queue_servers WHERE live=1
  </code></pre>
  
  <p>It works just fine.. But if I try to select the column "hostname" , or add it to the select column list, it won't use the live index unless I am searching for live=0 .. Why is this?</p>