title: index a bit field in MYSQL
body: <p>updated question:<br/>
  suppose the data I'm interested in is only those with field=1 and the actual ratio of data wheere field is 1 vs 0 is very small(eg. 1%)
  in this case, would index the field benefit my select where field =1 query?</p>
  
  <p>original question:<br/>
  I have a int field that will have either 0 or 1 value, would indexing this field speed up select queries such as:</p>
  
  <pre>
  select * from xxx where field=1;
  </pre>