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

@@ -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

mysql-test/r/endspace.result

@@ -154,7 +154,7 @@ teststring
 teststring
 explain select * from t1 order by text1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	key1	34	NULL	3	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	Using filesort
 alter table t1 modify text1 char(32) binary not null;
 select * from t1 order by text1;
 text1

mysql-test/r/group_by.result

@@ -1144,7 +1144,7 @@ CREATE TABLE t2 (a INT, b INT, KEY(a));
 INSERT INTO t2 VALUES (1, 1), (2, 2), (3,3), (4,4);
 EXPLAIN SELECT a, SUM(b) FROM t2 GROUP BY a LIMIT 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t2	index	NULL	a	5	NULL	4	
+1	SIMPLE	t2	index	NULL	a	5	NULL	2	
 EXPLAIN SELECT a, SUM(b) FROM t2 IGNORE INDEX (a) GROUP BY a LIMIT 2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	4	Using temporary; Using filesort

mysql-test/r/group_min_max.result

@@ -1963,20 +1963,20 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	128	Using temporary; Using filesort
 explain select a1,a2,count(a2) from t1 group by a1,a2,b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	idx_t1_1	163	NULL	128	Using index
+1	SIMPLE	t1	index	NULL	idx_t1_2	147	NULL	128	Using index
 explain extended select a1,a2,count(a2) from t1 where (a1 > 'a') group by a1,a2,b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	index	idx_t1_0,idx_t1_1,idx_t1_2	idx_t1_1	163	NULL	128	75.00	Using where; Using index
+1	SIMPLE	t1	index	idx_t1_0,idx_t1_1,idx_t1_2	idx_t1_2	147	NULL	128	75.00	Using where; Using index
 Warnings:
 Note	1003	select `test`.`t1`.`a1` AS `a1`,`test`.`t1`.`a2` AS `a2`,count(`test`.`t1`.`a2`) AS `count(a2)` from `test`.`t1` where (`test`.`t1`.`a1` > _latin1'a') group by `test`.`t1`.`a1`,`test`.`t1`.`a2`,`test`.`t1`.`b`
 explain extended select sum(ord(a1)) from t1 where (a1 > 'a') group by a1,a2,b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
-1	SIMPLE	t1	index	idx_t1_0,idx_t1_1,idx_t1_2	idx_t1_1	163	NULL	128	75.00	Using where; Using index
+1	SIMPLE	t1	index	idx_t1_0,idx_t1_1,idx_t1_2	idx_t1_2	147	NULL	128	75.00	Using where; Using index
 Warnings:
 Note	1003	select sum(ord(`test`.`t1`.`a1`)) AS `sum(ord(a1))` from `test`.`t1` where (`test`.`t1`.`a1` > _latin1'a') group by `test`.`t1`.`a1`,`test`.`t1`.`a2`,`test`.`t1`.`b`
 explain select distinct(a1) from t1 where ord(a2) = 98;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	idx_t1_1	163	NULL	128	Using where; Using index
+1	SIMPLE	t1	index	NULL	idx_t1_2	147	NULL	128	Using where; Using index
 select distinct(a1) from t1 where ord(a2) = 98;
 a1
 a
@@ -2256,7 +2256,7 @@ EXPLAIN SELECT 1 FROM t1 AS t1_outer WHERE
 a IN (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1_outer	index	NULL	a	10	NULL	15	Using where; Using index
-2	DEPENDENT SUBQUERY	t1	index	NULL	a	10	NULL	15	Using index
+2	DEPENDENT SUBQUERY	t1	index	NULL	a	10	NULL	1	Using index
 EXPLAIN SELECT 1 FROM t1 AS t1_outer GROUP BY a HAVING 
 a > (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

mysql-test/r/innodb.result

@@ -947,7 +947,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	#	
 explain select * from t1 order by b;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	index	NULL	b	4	NULL	#	
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using filesort
 explain select * from t1 order by c;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	#	Using filesort

mysql-test/r/innodb_mysql.result

@@ -851,13 +851,13 @@ EXPLAIN SELECT * FROM t1 WHERE b BETWEEN 1 AND 2 ORDER BY a;
 id	1
 select_type	SIMPLE
 table	t1
-type	range
+type	index
 possible_keys	bkey
-key	bkey
-key_len	5
+key	PRIMARY
+key_len	4
 ref	NULL
-rows	16
-Extra	Using where; Using index; Using filesort
+rows	32
+Extra	Using where; Using index
 SELECT * FROM t1 WHERE b BETWEEN 1 AND 2 ORDER BY a;
 a	b
 1	2
@@ -946,13 +946,13 @@ EXPLAIN SELECT * FROM t2 WHERE b=1 ORDER BY a;
 id	1
 select_type	SIMPLE
 table	t2
-type	ref
+type	index
 possible_keys	bkey
-key	bkey
-key_len	5
-ref	const
-rows	8
-Extra	Using where; Using index; Using filesort
+key	PRIMARY
+key_len	4
+ref	NULL
+rows	16
+Extra	Using where; Using index
 SELECT * FROM t2 WHERE b=1 ORDER BY a;
 a	b	c
 1	1	1

mysql-test/r/merge.result

@@ -86,7 +86,7 @@ a	b
 19	Testing
 explain select a from t3 order by a desc limit 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t3	index	NULL	a	4	NULL	1131	Using index
+1	SIMPLE	t3	index	NULL	a	4	NULL	10	Using index
 select a from t3 order by a desc limit 10;
 a
 699

mysql-test/r/order_by.result

@@ -1073,3 +1073,58 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	const	PRIMARY,b	b	5	const	1	
 1	SIMPLE	t2	ref	a	a	5	const	2	Using where; Using index
 DROP TABLE t1,t2;
+CREATE TABLE t1(
+id int auto_increment PRIMARY KEY, c2 int, c3 int, INDEX k2(c2), INDEX k3(c3));
+INSERT INTO t1 (c2,c3) VALUES
+(31,34),(35,38),(34,31),(32,35),(31,39),
+(11,14),(15,18),(14,11),(12,15),(11,19);
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+SELECT COUNT(*) FROM t1;
+COUNT(*)
+40960
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	k2	k3	5	NULL	88	Using where
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ref	k2	k2	5	const	9300	Using where; Using filesort
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 100;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index	k2	k3	5	NULL	316	Using where
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 2000;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	k2	k2	5	NULL	12937	Using where; Using filesort
+SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
+id	c3
+6	14
+16	14
+26	14
+36	14
+46	14
+56	14
+66	14
+76	14
+86	14
+96	14
+106	14
+116	14
+126	14
+136	14
+146	14
+156	14
+166	14
+176	14
+186	14
+196	14
+DROP TABLE t1;

mysql-test/r/select_found.result

@@ -84,7 +84,7 @@ UNIQUE KEY e_n (email,name)
 EXPLAIN SELECT SQL_CALC_FOUND_ROWS DISTINCT email FROM t2 LEFT JOIN t1  ON kid = t2.id WHERE t1.id IS NULL LIMIT 10;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	system	PRIMARY,kid	NULL	NULL	NULL	0	const row not found
-1	SIMPLE	t2	index	NULL	e_n	104	NULL	200	
+1	SIMPLE	t2	index	NULL	e_n	104	NULL	10	
 SELECT SQL_CALC_FOUND_ROWS DISTINCT email FROM t2 LEFT JOIN t1  ON kid = t2.id WHERE t1.id IS NULL LIMIT 10;
 email
 email1

mysql-test/r/subselect.result

@@ -3419,7 +3419,7 @@ EXPLAIN
 SELECT * FROM t1 WHERE (a,b) = ANY (SELECT a, max(b) FROM t1 GROUP BY a);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	9	Using where
-2	DEPENDENT SUBQUERY	t1	index	NULL	a	8	NULL	9	Using filesort
+2	DEPENDENT SUBQUERY	t1	index	NULL	a	8	NULL	1	Using filesort
 DROP TABLE t1;
 create table t1( f1 int,f2 int);
 insert into t1 values (1,1),(2,2);

mysql-test/t/distinct.test

@@ -97,7 +97,7 @@ explain SELECT t1.a from t1 group by a order by a desc;
 explain SELECT distinct t1.a from t1 order by a desc limit 1;
 explain SELECT distinct a from t3 order by a desc limit 2;
 explain SELECT distinct a,b from t3 order by a+1;
-explain SELECT distinct a,b from t3 order by a limit 10;
+explain SELECT distinct a,b from t3 order by a limit 2;
 explain SELECT a,b from t3 group by a,b order by a+1;
 
 drop table t1,t2,t3,t4;

mysql-test/t/order_by.test

@@ -739,3 +739,40 @@ INSERT INTO t2 VALUES (1,1),(1,2),(2,1),(2,2);
 EXPLAIN SELECT 1 FROM t1,t2 WHERE t1.b=2 AND t1.a=t2.a ORDER BY t2.b;
 
 DROP TABLE t1,t2;
+
+# End of 5.0
+
+#
+# Bug #28404: query with ORDER BY and ref access
+#
+
+CREATE TABLE t1(
+  id int auto_increment PRIMARY KEY, c2 int, c3 int, INDEX k2(c2), INDEX k3(c3));
+
+INSERT INTO t1 (c2,c3) VALUES
+ (31,34),(35,38),(34,31),(32,35),(31,39),
+ (11,14),(15,18),(14,11),(12,15),(11,19);
+
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
+
+SELECT COUNT(*) FROM t1;
+
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 100;
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 100;
+EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 2000;
+
+SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
+
+DROP TABLE t1;

sql/sql_select.h

@@ -194,6 +194,12 @@ typedef struct st_join_table {
   enum join_type type;
   bool		cached_eq_ref_table,eq_ref_table,not_used_in_distinct;
   bool		sorted;
+  /* 
+    If it's not 0 the number stored this field indicates that the index
+    scan has been chosen to access the table data and we expect to scan 
+    this number of rows for the table.
+  */ 
+  ha_rows       limit; 
   TABLE_REF	ref;
   JOIN_CACHE	cache;
   JOIN		*join;