title: Summary information column in mysql query
body: <p>I have a simple query:</p>
  
  <pre><code>SELECT sds.district_id,detail.year, detail.race, SUM(count)
  FROM school_data_race_ethnicity_raw as detail
  INNER JOIN school_data_schools as sds USING (school_id)
  GROUP BY district_id, year, race
  </code></pre>
  
  <p>Sample Result set:</p>
  
  <pre><code>| 68080104    | 2009 | Multiracial     |          0 |
  | 68080104    | 2009 | White           |        847 |
  | 68080104    | 2010 | American Indian |          1 |
  | 68080104    | 2010 | Asian           |          4 |
  | 68080104    | 2010 | Black           |         17 |
  | 68080104    | 2010 | Hispanic        |          4 |
  | 68080104    | 2010 | Multiracial     |          2 |
  | 68080104    | 2010 | White           |        823 |
  | 68080104    | 2011 | American Indian |          4 |
  | 68080104    | 2011 | Asian           |          4 |
  | 68080104    | 2011 | Black           |          9 |
  | 68080104    | 2011 | Hispanic        |         10 |
  | 68080104    | 2011 | Multiracial     |         24 |
  | 68080104    | 2011 | White           |        767 |
  +-------------+------+-----------------+------------+
  </code></pre>
  
  <p>I want to add a 5th column called total which displays a summation of the total population of for a given year and district. For example if I was in district 68080104 in 2011, the total would be (4+4+9+10+24+767). I need this as another column in this query. It also needs to be fast. (Under 10 seconds). I am struggling on how to do this and not compromise speed and data.</p>