1.  
  2. mysql> EXPLAIN SELECT day, sum(impressions) AS ti FROM daily_app_user_impressions, app_user_mappings WHERE daily_app_user_impressions.source_app_user_id = app_user_mappings.id AND app_user_mappings.app_id = 2 GROUP BY day ORDER BY day DESC;
  3. +----+-------------+----------------------------+------+-----------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------------------------------+------+---------------------------------+
  4. | id | select_type | TABLE                      | type | possible_keys                                                   | KEY                           | key_len | ref                                                                          | rows | Extra                           |
  5. +----+-------------+----------------------------+------+-----------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------------------------------+------+---------------------------------+
  6. |  1 | SIMPLE      | daily_app_user_impressions | ALL  | index_daily_app_user_impressions_on_source_app_user_id          | NULL                          | NULL    | NULL                                                                         |    1 | USING TEMPORARY; USING filesort | 
  7. |  1 | SIMPLE      | app_user_mappings          | ref  | index_app_user_mappings_on_id,index_app_user_mappings_on_app_id | index_app_user_mappings_on_id | 5       | archetypereporting_development.daily_app_user_impressions.source_app_user_id |    1 | USING WHERE                     | 
  8. +----+-------------+----------------------------+------+-----------------------------------------------------------------+-------------------------------+---------+------------------------------------------------------------------------------+------+---------------------------------+
  9. 2 rows IN SET (0.00 sec)
  10.