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, 4 insertions, 4 deletions

diff --git a/mysql-test/r/subselect_sj2_mat.result b/mysql-test/r/subselect_sj2_mat.result
index 5a9c3b90755..252f3c73a55 100644
--- a/mysql-test/r/subselect_sj2_mat.result
+++ b/mysql-test/r/subselect_sj2_mat.result
@@ -71,9 +71,9 @@ insert into t3 select a,a, a,a,a from t0;
 insert into t3 select a,a, a+100,a+100,a+100 from t0;
 explain select * from t3 where b in (select a from t1);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t3	ALL	b	NULL	NULL	NULL	20	
-1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	5	func	1	
-2	MATERIALIZED	t1	ALL	NULL	NULL	NULL	NULL	3	
+1	PRIMARY	<subquery2>	ALL	distinct_key	NULL	NULL	NULL	3	
+1	PRIMARY	t3	ref	b	b	5	test.t1.a	1	
+2	MATERIALIZED	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
 select * from t3 where b in (select a from t1);
 a	b	pk1	pk2	pk3
 1	1	1	1	1
@@ -880,9 +880,9 @@ SELECT * FROM t3 LEFT JOIN (v1,t2) ON t3.a = t2.a
 WHERE t3.b IN (SELECT b FROM t4);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	1	
+1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	5	func	1	
 1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	1	Using where
 1	PRIMARY	<derived3>	ALL	NULL	NULL	NULL	NULL	2	
-1	PRIMARY	<subquery2>	eq_ref	distinct_key	distinct_key	5	func	1	
 2	MATERIALIZED	t4	ALL	NULL	NULL	NULL	NULL	2	
 3	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	1	
 SELECT * FROM t3 LEFT JOIN (v1,t2) ON t3.a = t2.a