left out join

app/controllers/challenges_controller.rb

@@ -150,7 +150,7 @@ class ChallengesController < ApplicationController
     uid_logger("identifier: #{params}")
     # 通过调试发现 这里includes(:games)性能会慢10倍
     # @challenges = @shixun.challenges.fields_for_list
-    @challenges = Challenge.fields_for_list.includes(:games).where("challenges.shixun_id" => @shixun.id)
+    @challenges = Challenge.fields_for_list.left_outer_joins(:games).where("challenges.shixun_id" => @shixun.id)
 
     # @challenges = Challenge.includes(:games).where("games.user_id" => 12).where(shixun_id: @shixun.id)