课程搜索有问题

app/controllers/courses_controller.rb

@@ -87,7 +87,7 @@ class CoursesController < ApplicationController
         (course_members.role in(1,2,3) and CONCAT(users.lastname, users.firstname) like :keyword) or courses.name like :keyword
         or schools.name like :keyword
       }
-      @courses = @courses.left_joins(course_members: [user: [user_extension: :school]]).where("#{sql}", keyword: "%#{params[:search]}%")
+      @courses = @courses.left_outer_joins(course_members: [user: [user_extension: :school]]).where("#{sql}", keyword: "%#{params[:search]}%")
     end
     @courses_count = @courses.size