调整

db/migrate/20200111024736_add_index_for_subject_records.rb

@@ -1,6 +1,6 @@
 class AddIndexForSubjectRecords < ActiveRecord::Migration[5.2]
   def change
-    remove_index :subject_records, :subject_id
+    # remove_index :subject_records, :subject_id
     add_index :subject_records, :subject_id, unique: true
   end
 end