code: function (order) {
              var ret = order;
              if (order) {
                  ret = order.map(function (o) {
                      if (isInstanceOf(o, OrderedExpression)) {
                          return o.invert();
                      } else {
                          return new OrderedExpression(isString(o) ? new Identifier(o) : o);
                      }
                  }, this);
              }
              return ret;
          }
docs: @private
  Inverts the given order by breaking it into a list of column references
  and inverting them.
  
  ds.invertOrder([sql.identifier("id").desc()]]) //=> [id]
  ds.invertOrder("category", sql.identifier("price").desc()]) #=> [category.desc(), price]