MySQL - on which columns to use indexes
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I have a query like this:


    SELECT 
      `Games`.`id`, `Games`.`name`, `Games`.`url` 
    FROM 
      `Games`
    LEFT JOIN 
      `GamesRuns` 
    ON 
      Games.id = GamesRuns.game_id 
    WHERE 
      (GamesRuns.date >= '2012-07-17 13:14:08') AND (Games.score = 0) AND (Games.active = 1) AND (Games.display = 1) 
    GROUP BY 
      `Games`.`id` 
    ORDER BY 
      SUM(GamesRuns.count) DESC 
    LIMIT 5;

I want to ask on which columns I should put indexes. I think it should be on GamesRuns.date and Games.score + Games.active + Games.display as multiindex. And I think that to put an index on GamesRuns.count is pointless because it's in SUM function, but otherwise (without SUM function) there should be also an index. Is it right? Because when I use EXPLAIN, it shows me that possible_key and also key is PRIMARY, but PRIMARY is just Games.id. Thank you for your answer.