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, 12 insertions, 0 deletions

diff --git a/mysql-test/t/subselect.test b/mysql-test/t/subselect.test
index 2540232bd3b..9d87cbc486c 100644
--- a/mysql-test/t/subselect.test
+++ b/mysql-test/t/subselect.test
@@ -3248,6 +3248,10 @@ DROP TABLE t1, t2, t3;
 # Bug#30788 Inconsistent retrieval of char/varchar
 #
 
+SET @save_optimizer_switch=@@optimizer_switch;
+SET optimizer_switch='semijoin_with_cache=off';
+SET optimizer_switch='materialization=off';
+
 CREATE TABLE t1 (a CHAR(1), b VARCHAR(10));
 INSERT INTO t1 VALUES ('a', 'aa');
 INSERT INTO t1 VALUES ('a', 'aaa');
@@ -3269,6 +3273,7 @@ SELECT a,b FROM t1 WHERE b IN (SELECT a FROM t1 WHERE LENGTH(a)<500);
 
 DROP TABLE t1,t2;
 
+SET optimizer_switch= @save_optimizer_switch;
 
 #
 # Bug#32400 Complex SELECT query returns correct result only on some occasions
@@ -3418,8 +3423,11 @@ drop table t1, t2;
 
 CREATE TABLE t1 (a INT);
 INSERT INTO t1 VALUES (1),(2);
+SET @save_join_cache_level=@@join_cache_level;
+SET join_cache_level=0;
 EXPLAIN EXTENDED SELECT 1 FROM t1 WHERE 1 IN (SELECT min(a) FROM t1 GROUP BY a);
 EXPLAIN EXTENDED SELECT 1 FROM t1 WHERE 1 IN (SELECT min(a) FROM t1 WHERE a > 3 GROUP BY a);
+SET join_cache_level=@save_join_cache_level;
 DROP TABLE t1;
 
 --echo #
@@ -4430,8 +4438,12 @@ INSERT INTO t2 VALUES (11,1);
 INSERT INTO t2 VALUES (12,2);
 INSERT INTO t2 VALUES (15,4);
 
+
+SET @save_join_cache_level=@@join_cache_level;
+SET join_cache_level=0;
 EXPLAIN SELECT * FROM t1 WHERE pk IN (SELECT it.pk FROM t2 JOIN t2 AS it ON 1);
 SELECT * FROM t1 WHERE pk IN (SELECT it.pk FROM t2 JOIN t2 AS it ON 1);
+SET join_cache_level=@save_join_cache_level;
 
 DROP table t1,t2;