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, 1 insertions, 1 deletions

diff --git a/mysql-test/main/subselect_sj_mat.result b/mysql-test/main/subselect_sj_mat.result
index 9e1870875ce..6a4a1a4ad5b 100644
--- a/mysql-test/main/subselect_sj_mat.result
+++ b/mysql-test/main/subselect_sj_mat.result
@@ -1963,7 +1963,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	100.00	Using where; Using join buffer (flat, BNL join)
 2	MATERIALIZED	t2	ALL	NULL	NULL	NULL	NULL	3	100.00	
 Warnings:
-Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from  <materialize> (/* select#2 */ select max(`test`.`t2`.`c`) from `test`.`t2`) join `test`.`t1` where `test`.`t1`.`b` = 7 and `test`.`t1`.`a` = `<subquery2>`.`MAX(c)` and (<cache>(`<subquery2>`.`MAX(c)` is null) or `<subquery2>`.`MAX(c)` = 7)
+Note	1003	/* select#1 */ select `test`.`t1`.`a` AS `a`,`test`.`t1`.`b` AS `b` from  <materialize> (/* select#2 */ select max(`test`.`t2`.`c`) from `test`.`t2` having `MAX(c)` is null or `MAX(c)` = 7) join `test`.`t1` where `test`.`t1`.`b` = 7 and `test`.`t1`.`a` = `<subquery2>`.`MAX(c)` and (<cache>(`<subquery2>`.`MAX(c)` is null) or `<subquery2>`.`MAX(c)` = 7)
 SELECT * FROM t1
 WHERE a IN (SELECT MAX(c) FROM t2) AND b=7 AND (a IS NULL OR a=b);
 a	b