_increment_attribute

# File activerecord/lib/active_record/relation.rb, line 884
      def _increment_attribute(attribute, value = 1)
        bind = predicate_builder.build_bind_attribute(attribute.name, value.abs)
        expr = table.coalesce(Arel::Nodes::UnqualifiedColumn.new(attribute), 0)
        expr = value < 0 ? expr - bind : expr + bind
        expr.expr
      end