Fixed bug#28404.

This patch adds cost estimation for the queries with ORDER BY / GROUP BY
and LIMIT. 
If there was a ref/range access to the table whose rows were required
to be ordered in the result set the optimizer always employed this access
though a scan by a different index that was compatible with the required 
order could be cheaper to produce the first L rows of the result set.
Now for such queries the optimizer makes a choice between the cheapest
ref/range accesses not compatible with the given order and index scans
compatible with it.


mysql-test/r/distinct.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/endspace.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/group_by.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/group_min_max.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/innodb.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/innodb_mysql.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/merge.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/order_by.result:
  Added a test case for bug #28404.
mysql-test/r/select_found.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/r/subselect.result:
  Adjusted results for test cases affected fy the fix for bug #28404.
mysql-test/t/distinct.test:
  Changed a test case after adding the fix for bug #28404.
mysql-test/t/order_by.test:
  Added a test case for bug #28404.
sql/sql_select.cc:
  Fixed bug#28404.
  This patch adds cost estimation for the queries with ORDER BY / GROUP BY
  and LIMIT. 
  Now for such queries the optimizer makes a choice between the cheapest
  ref/range accesses not compatible with the given order and index scans
  compatible with it.
  
  Modified the function test_if_skip_sort_order to make the above mentioned
  choice cost based.
sql/sql_select.h:
  Fixed bug#28404.
  This patch adds cost estimation for the queries with ORDER BY / GROUP BY
  and LIMIT. 
  Added a new field fot the JOIN_TAB structure.

1 files changed, 4 insertions, 4 deletions

diff --git a/mysql-test/r/distinct.result b/mysql-test/r/distinct.result
index 002dbc6ccb5..795d8956a08 100644
--- a/mysql-test/r/distinct.result
+++ b/mysql-test/r/distinct.result
@@ -209,16 +209,16 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
 explain SELECT distinct t1.a from t1 order by a desc limit 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	4	Using index
+1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	1	Using index
 explain SELECT distinct a from t3 order by a desc limit 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	index	NULL	a	5	NULL	204	Using index
+1	SIMPLE	t3	index	NULL	a	5	NULL	40	Using index
 explain SELECT distinct a,b from t3 order by a+1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	204	Using temporary; Using filesort
-explain SELECT distinct a,b from t3 order by a limit 10;
+explain SELECT distinct a,b from t3 order by a limit 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	index	NULL	a	5	NULL	204	Using temporary
+1	SIMPLE	t3	index	NULL	a	5	NULL	2	Using temporary
 explain SELECT a,b from t3 group by a,b order by a+1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t3	ALL	NULL	NULL	NULL	NULL	204	Using temporary; Using filesort