change migration

db/migrate/20200228052609_create_notification_statistics.rb

@@ -11,10 +11,8 @@ class CreateNotificationStatistics < ActiveRecord::Migration[5.2]
       t.integer :app_type, comment: "版本" # 调用接口时 app_type
       t.string :device_model, comment: "设备型号" # APP 上报
       t.string :ip, comment: "IP地址" # 可能拿不到
-      t.datetime :created_at
-      t.datetime :updated_at
 
-      t.timestamps null: false
+      t.timestamps
     end
   end
 end