新しい列の文字列を使用したSQLGroupBY

eventsに参加できます resultsからの2つのクエリに関する表 テーブル、クラスごとに1つ：

SELECT    event_data, class_40_winner, class_30_winner
FROM      events e
LEFT JOIN (SELECT result_event, name AS class_40_winner
           FROM   results 
           WHERE  class = 40 AND position = 1) c40 ON e.id = c40.result_event
LEFT JOIN (SELECT result_event, name AS class_30_winner
           FROM   results 
           WHERE  class = 30 AND position = 1) c30 ON e.id = c30.result_event