SQL Group BY ved hjælp af strenge i nye kolonner

Du kan deltage i events tabel på to forespørgsler fra results tabel, en for hver klasse:

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