为student_work_tests增加索引

db/migrate/20160907055119_add_index_to_student_work_tests.rb

@@ -0,0 +1,5 @@
+class AddIndexToStudentWorkTests < ActiveRecord::Migration
+  def change
+    add_index :student_work_tests, :student_work_id
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended to check this file into your version control system.
 
-ActiveRecord::Schema.define(:version => 20160830090214) do
+ActiveRecord::Schema.define(:version => 20160907055119) do
 
   create_table "activities", :force => true do |t|
     t.integer  "act_id",                                  :null => false
@@ -1829,6 +1829,8 @@ ActiveRecord::Schema.define(:version => 20160830090214) do
     t.text     "src"
   end
 
+  add_index "student_work_tests", ["student_work_id"], :name => "index_student_work_tests_on_student_work_id"
+
   create_table "student_works", :force => true do |t|
     t.string   "name"
     t.text     "description",             :limit => 2147483647