调整

app/controllers/courses_controller.rb

@@ -104,7 +104,7 @@ class CoursesController < ApplicationController
   def course_videos
     videos = @course.videos
     if params[:category_id].present? && params[:category_id].to_i != 0
-      videos = videos.where(course_second_category_id: params[:category_id].to_i)
+      videos = videos.where(course_videos: {course_second_category_id: params[:category_id].to_i})
     end
 
     videos = custom_sort(videos, params[:sort_by], params[:sort_direction])