Back-ported the patch of the mysql-5.6 code line that

fixed several defects in the greedy optimization:

1) The greedy optimizer calculated the 'compare-cost' (CPU-cost)
   for iterating over the partial plan result at each level in
   the query plan as 'record_count / (double) TIME_FOR_COMPARE'

   This cost was only used locally for 'best' calculation at each
   level, and *not* accumulated into the total cost for the query plan.

   This fix added the 'CPU-cost' of processing 'current_record_count'
   records at each level to 'current_read_time' *before* it is used as
   'accumulated cost' argument to recursive 
   best_extension_by_limited_search() calls. This ensured that the
   cost of a huge join-fanout early in the QEP was correctly
   reflected in the cost of the final QEP.

   To get identical cost for a 'best' optimized query and a
   straight_join with the same join order, the same change was also
   applied to optimize_straight_join() and get_partial_join_cost()

2) Furthermore to get equal cost for 'best' optimized query and a
   straight_join the new code substrcated the same '0.001' in
   optimize_straight_join() as it had been already done in
   best_extension_by_limited_search()

3) When best_extension_by_limited_search() aggregated the 'best' plan a
   plan was 'best' by the check :

   'if ((search_depth == 1) || (current_read_time < join->best_read))'

   The term '(search_depth == 1' incorrectly caused a new best plan to be
   collected whenever the specified 'search_depth' was reached - even if
   this partial query plan was more expensive than what we had already
   found.

1 files changed, 7 insertions, 4 deletions

diff --git a/mysql-test/r/subselect4.result b/mysql-test/r/subselect4.result
index f9337ddc78a..6c942bca31a 100644
--- a/mysql-test/r/subselect4.result
+++ b/mysql-test/r/subselect4.result
@@ -1226,22 +1226,25 @@ CREATE TABLE t4 (c1 varchar(1) primary key);
 INSERT INTO t4 VALUES ('k'), ('d');
 SET @save_optimizer_switch=@@optimizer_switch;
 SET optimizer_switch='outer_join_with_cache=off';
+SET optimizer_switch='semijoin_with_cache=off';
+SET optimizer_switch='materialization=off';
 EXPLAIN
 SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	0	const row not found
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; FirstMatch(t2); Using join buffer (flat, BNL join)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; FirstMatch(t1)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using join buffer (flat, BNL join)
 SELECT * FROM t1 RIGHT JOIN t2 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
 c1	c1
 EXPLAIN
 SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	0	const row not found
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; FirstMatch(t2); Using join buffer (flat, BNL join)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where; FirstMatch(t1)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using join buffer (flat, BNL join)
 SELECT * FROM t2 LEFT JOIN t1 ON t1.c1 WHERE 's' IN (SELECT c1 FROM t2);
 c1	c1
+SET optimizer_switch='materialization=on';
 EXPLAIN
 SELECT * FROM (t2 LEFT JOIN t1 ON t1.c1) LEFT JOIN t3 on t3.c1 WHERE 's' IN (SELECT c1 FROM t2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra