我之前也遇到过同样的问题，我根据这里解决了 https://github.com/rails/rails/pull/13247#issuecomment-32425844

I had a same problem before, and I solved according to here https://github.com/rails/rails/pull/13247#issuecomment-32425844

使用Rails 2.3.5，MySQL 5.7.9版本和mysql gem需要具备 此位用作初始化程序 config/initializers/abstract_mysql_adapter.rb:

With Rails 2.3.5, MySQL version 5.7.9 and mysql gem you need to have this bit as an initializer in config/initializers/abstract_mysql_adapter.rb:

class ActiveRecord::ConnectionAdapters::MysqlAdapter
  NATIVE_DATABASE_TYPES[:primary_key] = "int(11) auto_increment PRIMARY KEY"
end

对于mysql2，它应该是config/initializers/abstract_mysql2_adapter.rb:

For mysql2, it should be config/initializers/abstract_mysql2_adapter.rb:

class ActiveRecord::ConnectionAdapters::Mysql2Adapter
  NATIVE_DATABASE_TYPES[:primary_key] = "int(11) auto_increment PRIMARY KEY"
end