迁移错误 - 错误：您的 SQL 语法有错误；检查相应的手册答案

【问题标题】：Error in migration - Error: You have an error in your SQL syntax; check the manual that corresponds迁移错误 - 错误：您的 SQL 语法有错误；检查相应的手册
【发布时间】：2015-07-10 14:47:00
【问题描述】：

无法理解语法 sql 文件迁移有什么问题。请帮忙：

我运行 rake db:migrate

错误：

Mysql2::Error: 你的 SQL 语法有错误；检查与您的 MySQL 服务器版本相对应的手册，以在第 1 行的 ')' 附近使用正确的语法： UPDATE photos SET votes_count = 0, rating = 0 WHERE id NOT IN ()/home/user/myapp/appmame/db /migrate/20131110162613_recalculate_photos_rating.rb:8:in `up'

class RecalculatePhotosRating < ActiveRecord::Migration
  def up
    if Vote.where("subject_type='Photo' and rating > 1").count > 0
      ActiveRecord::Base.connection.execute "DELETE FROM votes WHERE subject_type='Photo' AND rating <= 5"
      ActiveRecord::Base.connection.execute "UPDATE votes SET rating=1 WHERE subject_type='Photo'"
    end
    pids = Vote.where(subject_type: 'Photo').pluck(:subject_id).uniq
    ActiveRecord::Base.connection.execute "UPDATE photos SET votes_count = 0, rating = 0 WHERE id NOT IN (#{pids.join(', ')})"
    ActiveRecord::Base.connection.execute "UPDATE photos SET rating=(SELECT COUNT(*) FROM votes WHERE votes.subject_type='Photo' AND subject_id=photos.id) WHERE id IN (#{pids.join(', ')})"
    ActiveRecord::Base.connection.execute "UPDATE photos SET votes_count=(SELECT COUNT(*) FROM votes WHERE votes.subject_type='Photo' AND subject_id=photos.id) WHERE id IN (#{pids.join(', ')})"
  end

  def down
  end
end

【问题讨论】：

标签： mysql ruby-on-rails mysql2

【解决方案1】：

您必须检查pids 查询是否返回空结果：

class RecalculatePhotosRating < ActiveRecord::Migration
  def up
    if Vote.where("subject_type='Photo' and rating > 1").count > 0
      ActiveRecord::Base.connection.execute "DELETE FROM votes WHERE subject_type='Photo' AND rating <= 5"
      ActiveRecord::Base.connection.execute "UPDATE votes SET rating=1 WHERE subject_type='Photo'"
    end
    pids = Vote.where(subject_type: 'Photo').pluck(:subject_id).uniq
    unless pids.empty?
      ActiveRecord::Base.connection.execute "UPDATE photos SET votes_count = 0, rating = 0 WHERE id NOT IN (#{pids.join(', ')})"
      ActiveRecord::Base.connection.execute "UPDATE photos SET rating=(SELECT COUNT(*) FROM votes WHERE votes.subject_type='Photo' AND subject_id=photos.id) WHERE id IN (#{pids.join(', ')})"
      ActiveRecord::Base.connection.execute "UPDATE photos SET votes_count=(SELECT COUNT(*) FROM votes WHERE votes.subject_type='Photo' AND subject_id=photos.id) WHERE id IN (#{pids.join(', ')})"
    end
  end

  def down
  end
end

【讨论】：

我插入了除非 pids.empty？又是同样的错误。