```ruby
class RemovePublishedArticles < ActiveRecord::Migration
  def self.up
    select_all("SELECT * from articles WHERE type = 'PublishedArticle'").each do |published|
      reference = select('select * from articles where id = %d' % published['reference_article_id']).first
      if reference
        execute(ActiveRecord::Base.sanitize_sql(["UPDATE articles SET type = ?, abstract = ?, body = ? WHERE articles.id  = ?", reference['type'], reference['abstract'], reference['body'], published['id']]))
      else
        execute("DELETE from articles where articles.id  = #{published['id']}")
      end
    end
  end

  def self.down
    say 'Nothing to do'
  end
end
```

Use the proper method for selecting from the database
user
```ruby
class RemovePublishedArticles < ActiveRecord::Migration
  def self.up
    select_all("SELECT * from articles WHERE type = 'PublishedArticle'").each do |published|
      reference = select_one('select * from articles where id = %d' % published['reference_article_id'])
      if reference
        execute(ActiveRecord::Base.sanitize_sql(["UPDATE articles SET type = ?, abstract = ?, body = ? WHERE articles.id  = ?", reference['type'], reference['abstract'], reference['body'], published['id']]))
      else
        execute("DELETE from articles where articles.id  = #{published['id']}")
      end
    end
  end

  def self.down
    say 'Nothing to do'
  end
end
```
assistant