code: def _join(self, node):
          
  
          select_block = str(node.attributes)
          from_block = '{left} {operator} {right}'.format(
              left=self._join_helper(node.left),
              right=self._join_helper(node.right),
              operator=self._get_sql_operator(node))
  
          if node.operator == Operator.theta_join:
              from_block = '{from_block} ON {conditions}'.format(
                  from_block=from_block,
                  conditions=node.conditions)
  
          return self.query(select_block, from_block, '')
docs: Translate a join node into SQLQuery.
          :param node: a treebrd node
          :return: a SQLQuery object for the tree rooted at node