diff --git a/app/controllers/poll_votes_controller.rb b/app/controllers/poll_votes_controller.rb
index 4a15ae301..a2a5bf8c3 100644
--- a/app/controllers/poll_votes_controller.rb
+++ b/app/controllers/poll_votes_controller.rb
@@ -10,7 +10,7 @@ class PollVotesController < ApplicationController
       begin
         question_votes = @poll_question.poll_votes
         question_type = @poll_question.question_type
-        question_answer_id = params[:poll_answer_id] ? params[:poll_answer_id] : nil #该答案的id
+        question_answer_id = params[:poll_answer_id] ? params[:poll_answer_id] : -1 #该答案的id
         question_answer_text = params[:vote_text].present? ? params[:vote_text] : nil    #其他选项的内容
         user_votes = question_votes.find_current_vote("user_id",current_user.id) #当前用户的答案，可能有多个
         # 当前用户的当前答案，如果已存在，当再次点击的时候，取消答案，即删除该答案
diff --git a/db/migrate/20191203040140_add_uniq_index_to_poll_votes.rb b/db/migrate/20191203040140_add_uniq_index_to_poll_votes.rb
new file mode 100644
index 000000000..cdf94647a
--- /dev/null
+++ b/db/migrate/20191203040140_add_uniq_index_to_poll_votes.rb
@@ -0,0 +1,16 @@
+class AddUniqIndexToPollVotes < ActiveRecord::Migration[5.2]
+  def change
+    remove_index :poll_votes, column: [:poll_question_id, :user_id]
+
+    change_column_default :poll_votes, :poll_question_id, from: nil, to: -1
+    PollVote.where(poll_answer_id: nil).update_all(poll_answer_id: -1)
+
+    sql = %Q(delete from poll_votes where (poll_question_id, user_id, poll_answer_id) in
+            (select * from (select poll_question_id, user_id, poll_answer_id from poll_votes group by poll_question_id, user_id, poll_answer_id having count(*) > 1) a)
+            and id not in (select * from (select min(id) from poll_votes group by poll_question_id, user_id, poll_answer_id having count(*) > 1 order by id) b))
+    ActiveRecord::Base.connection.execute sql
+
+    add_index :poll_votes, [:poll_question_id, :user_id, :poll_answer_id], name: 'poll_answer_index', unique: true
+
+  end
+end