Now above query first materialize whole view an then start joining, when the size of materialized table could be reduced by pushing conditions related to the view it its HAVING clause.
1. 'strip' view field references when pushed into lower SELECT (SELECT of the view)
2. ref_pointer_array predefined size
1. Clone() method should be done for most (all) items to be able to construct expression for pusing down to the VIEW
2. If we will construct whole item tree then fields for view should be substituted by its translation table entry (also cloned?).
3. It is better to avoid pushing subqueries down to the VIEW because it requre resorting SELECT_LEX tree.
4. for UNION based VIEW condition can be pushed to fake select HAVING.
5. All transformation shouldbe rolled back before next execution.