id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	tournament_stage_games	NULL	index_merge	fk_tournament_stage_games_first_player_id,fk_tournament_stage_games_second_player_id,fk_tournament_stage_games_tournament_id,fk_tournament_stage_games_use_stage_id	fk_tournament_stage_games_first_player_id,fk_tournament_stage_games_second_player_id	5,5	NULL	5	1	Using union(fk_tournament_stage_games_first_player_id,fk_tournament_stage_games_second_player_id); Using where; Using filesort