MDEV-12387 Push conditions into materialized subqueries

The logic and the implementation scheme are similar with the
MDEV-9197 Pushdown conditions into non-mergeable views/derived tables

How the push down is made on the example:

select * from t1
where a>3 and b>10 and
 (a,b) in (select x,max(y) from t2 group by x);

-->

select * from t1
where a>3 and b>10 and
  (a,b) in (select x,max(y)
            from t2
            where x>3
            group by x
            having max(y)>10);

The implementation scheme:

1. Search for the condition cond that depends only on the fields
   from the left part of the IN subquery (left_part)
2. Find fields F_group in the select of the right part of the
   IN subquery (right_part) that are used in the GROUP BY
3. Extract from the cond condition cond_where that depends only on the
   fields from the left_part that stay at the same places in the left_part
   (have the same indexes) as the F_group fields in the projection of the
   right_part
4. Transform cond_where so it can be pushed into the WHERE clause of the
   right_part and delete cond_where from the cond
5. Transform cond so it can be pushed into the HAVING clause of the right_part

The optimization is made in the
Item_in_subselect::pushdown_cond_for_in_subquery() and is controlled by the
variable condition_pushdown_for_subquery.

New test file in_subq_cond_pushdown.test is created.

There are also some changes made for setup_jtbm_semi_joins().
Now it is decomposed into the 2 procedures: setup_degenerate_jtbm_semi_joins()
that is called before optimize_cond() for cond and setup_jtbm_semi_joins()
that is called after optimize_cond().
New setup_jtbm_semi_joins() is made in the way so that the result of its work is
the same as if it was called before optimize_cond().

The code that is common for pushdown into materialized derived and into materialized
IN subqueries is factored out into pushdown_cond_for_derived(),
Item_in_subselect::pushdown_cond_for_in_subquery() and
st_select_lex::pushdown_cond_into_where_clause().

1 files changed, 9 insertions, 2 deletions

diff --git a/sql/opt_subselect.h b/sql/opt_subselect.h
index 9cb19e0cc6c..031118288b9 100644
--- a/sql/opt_subselect.h
+++ b/sql/opt_subselect.h
@@ -26,8 +26,15 @@ int check_and_do_in_subquery_rewrites(JOIN *join);
 bool convert_join_subqueries_to_semijoins(JOIN *join);
 int pull_out_semijoin_tables(JOIN *join);
 bool optimize_semijoin_nests(JOIN *join, table_map all_table_map);
-bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,  
-                           Item **join_where);
+Item *and_new_conditions_to_optimized_cond(THD *thd, Item *cond,
+                                           COND_EQUAL **cond_eq,
+                                           List<Item> &new_conds,
+                                           Item::cond_result *cond_value);
+bool setup_degenerate_jtbm_semi_joins(JOIN *join,
+                                      List<TABLE_LIST> *join_list,
+                                      List<Item> &eq_list);
+bool setup_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list,
+                           List<Item> &eq_list);
 void cleanup_empty_jtbm_semi_joins(JOIN *join, List<TABLE_LIST> *join_list);
 
 // used by Loose_scan_opt