configure_connection

# File activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb, line 825
      def configure_connection
        variables = @config.fetch(:variables, {}).stringify_keys

        # By default, MySQL 'where id is null' selects the last inserted id.
        # Turn this off. http://dev.rubyonrails.org/ticket/6778
        variables['sql_auto_is_null'] = 0

        # Increase timeout so the server doesn't disconnect us.
        wait_timeout = @config[:wait_timeout]
        wait_timeout = 2147483 unless wait_timeout.is_a?(Fixnum)
        variables['wait_timeout'] = self.class.type_cast_config_to_integer(wait_timeout)

        # Make MySQL reject illegal values rather than truncating or blanking them, see
        # http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html#sqlmode_strict_all_tables
        # If the user has provided another value for sql_mode, don't replace it.
        unless variables.has_key?('sql_mode')
          variables['sql_mode'] = strict_mode? ? 'STRICT_ALL_TABLES' : ''
        end

        # NAMES does not have an equals sign, see
        # http://dev.mysql.com/doc/refman/5.0/en/set-statement.html#id944430
        # (trailing comma because variable_assignments will always have content)
        if @config[:encoding]
          encoding = "NAMES #{@config[:encoding]}"
          encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
          encoding << ", "
        end

        # Gather up all of the SET variables...
        variable_assignments = variables.map do |k, v|
          if v == ':default' || v == :default
            "@@SESSION.#{k} = DEFAULT" # Sets the value to the global or compile default
          elsif !v.nil?
            "@@SESSION.#{k} = #{quote(v)}"
          end
          # or else nil; compact to clear nils out
        end.compact.join(', ')

        # ...and send them all in one query
        @connection.query  "SET #{encoding} #{variable_assignments}"
      end