pk_and_sequence_for

# File activerecord/lib/active_record/connection_adapters/mysql_adapter.rb, line 534
      def pk_and_sequence_for(table) #:nodoc:
        keys = []
        result = execute("describe #{quote_table_name(table)}")
        result.each_hash do |h|
          keys << h["Field"]if h["Key"] == "PRI"
        end
        result.free
        keys.length == 1 ? [keys.first, nil] : nil
      end