Change cost for REF to take into account cost for 1 extra key read_next

The main difference in code path between EQ_REF and REF is that for
REF we have to do an extra read_next on the index to check that there
is no more matching rows.

Before this patch we added a preference of EQ_REF by ensuring that REF
would always estimate to find at least 2 rows.

This patch adds the cost of the extra key read_next to REF access and
removes the code that limited REF to at least 2 rows. For some queries
this can have a big effect as the total estimated rows will be halved
for each REF table with 1 rows.

multi_range cost calculations are also changed to take into account
the difference between EQ_REF and REF.

The effect of the patch to the test suite:
- About 80 test case changed
- Almost all changes where for EXPLAIN where estimated rows for REF
  where changed from 2 to 1.
- A few test cases using explain extended had a change of 'filtered'.
  This is because of the estimated rows are now closer to the
  calculated selectivity.
- A very few test had a change of table order.
  This is because the change of estimated rows from 2 to 1 or the small
  cost change for REF
  (main.subselect_sj_jcl6, main.group_by, main.dervied_cond_pushdown,
  main.distinct, main.join_nested, main.order_by, main.join_cache)
- No key statistics and the estimated rows are now smaller which cased
  estimated filtering to be lower.
  (main.subselect_sj_mat)
- The number of total rows are halved.
  (main.derived_cond_pushdown)
- Plans with 1 row changed to use RANGE instead of REF.
  (main.group_min_max)
- ALL changed to REF
  (main.key_diff)
- Key changed from ref + index_only to PRIMARY key for InnoDB, as
  OPTIMIZER_ROW_LOOKUP_COST + OPTIMIZER_ROW_NEXT_FIND_COST is smaller than
  OPTIMIZER_KEY_LOOKUP_COST + OPTIMIZER_KEY_NEXT_FIND_COST.
  (main.join_outer_innodb)
- Cost changes printouts
  (main.opt_trace*)
- Result order change
  (innodb_gis.rtree)

mysql-test/main/subselect_sj.result

@@ -502,7 +502,7 @@ EXPLAIN EXTENDED SELECT vkey FROM t0 WHERE pk IN
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	PRIMARY	t0	ALL	PRIMARY	NULL	NULL	NULL	5	100.00	
 1	PRIMARY	t1	eq_ref	PRIMARY	PRIMARY	4	test.t0.pk	1	100.00	Using where
-1	PRIMARY	t2	ref	vkey	vkey	4	test.t1.vnokey	2	50.00	Using index; FirstMatch(t1)
+1	PRIMARY	t2	ref	vkey	vkey	4	test.t1.vnokey	1	100.00	Using index; FirstMatch(t1)
 Warnings:
 Note	1003	select `test`.`t0`.`vkey` AS `vkey` from `test`.`t0` `t1` semi join (`test`.`t0` `t2`) join `test`.`t0` where `test`.`t1`.`pk` = `test`.`t0`.`pk` and `test`.`t2`.`vkey` = `test`.`t1`.`vnokey`
 SELECT vkey FROM t0 WHERE pk IN 
@@ -2154,7 +2154,7 @@ explain
 SELECT * FROM t1, t2 WHERE (t2.a , t1.b) IN (SELECT a, b FROM t3);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	2	Using where
-1	PRIMARY	t3	ref	b	b	5	test.t1.b	2	Using where; Start temporary
+1	PRIMARY	t3	ref	b	b	5	test.t1.b	1	Using where; Start temporary
 1	PRIMARY	t2	eq_ref	PRIMARY	PRIMARY	4	test.t3.a	1	Using index; End temporary
 SELECT * FROM t1, t2 WHERE (t2.a , t1.b) IN (SELECT a, b FROM t3);
 b	a
@@ -2179,7 +2179,7 @@ explain
 SELECT * FROM t3 WHERE t3.a IN (SELECT t5.a FROM t2, t4, t5 WHERE t2.c = t5.a AND t2.b = t5.b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t5	index	a	a	10	NULL	2	Using where; Using index; Start temporary
-1	PRIMARY	t2	ref	b	b	5	test.t5.b	2	Using where
+1	PRIMARY	t2	ref	b	b	5	test.t5.b	1	Using where
 1	PRIMARY	t4	ALL	NULL	NULL	NULL	NULL	3	
 1	PRIMARY	t3	ALL	NULL	NULL	NULL	NULL	15	Using where; End temporary; Using join buffer (flat, BNL join)
 SELECT * FROM t3 WHERE t3.a IN (SELECT t5.a FROM t2, t4, t5 WHERE t2.c = t5.a AND t2.b = t5.b);
@@ -2436,9 +2436,9 @@ SET SESSION optimizer_switch='loosescan=off';
 EXPLAIN
 SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
-1	PRIMARY	t2	range	idx	idx	4	NULL	2	Using where; Using index
-1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index; FirstMatch(t1)
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where
+1	PRIMARY	t3	range	idx	idx	4	NULL	2	Using where; Using index
+1	PRIMARY	t2	ref	idx	idx	9	test.t3.b,test.t1.a	1	Using index; FirstMatch(t1)
 SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
 a
 5
@@ -2446,9 +2446,9 @@ SET SESSION optimizer_switch='loosescan=on';
 EXPLAIN
 SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	
-1	PRIMARY	t2	range	idx	idx	4	NULL	2	Using where; Using index
-1	PRIMARY	t3	ref	idx	idx	4	test.t2.b	1	Using index; FirstMatch(t1)
+1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	4	Using where
+1	PRIMARY	t3	range	idx	idx	4	NULL	2	Using where; Using index
+1	PRIMARY	t2	ref	idx	idx	9	test.t3.b,test.t1.a	1	Using index; FirstMatch(t1)
 SELECT * FROM t1 WHERE a IN (SELECT t2.a FROM t2,t3 WHERE t2.b = t3.b);
 a
 5
@@ -2561,7 +2561,7 @@ INSERT INTO t1 VALUES
 (6,3),(7,1),(8,4),(9,3),(10,2);
 CREATE TABLE t2 ( c INT, d INT, KEY(c) );
 INSERT INTO t2 VALUES
-(1,2),(2,1),(3,3),(4,2),(5,5),(6,3),(7,1);
+(1,2),(2,1),(3,3),(4,2),(5,5),(6,3),(7,1),(11,11);
 analyze table t1,t2;
 Table	Op	Msg_type	Msg_text
 test.t1	analyze	status	Engine-independent statistics collected
@@ -2571,15 +2571,15 @@ test.t2	analyze	status	OK
 explain
 SELECT a, b, d FROM t1, t2
 WHERE ( b, d ) IN
-( SELECT b, d FROM t1, t2 WHERE b = c );
+( SELECT b, d FROM t1 as t3, t2 as t4 WHERE b = c );
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	PRIMARY	t1	index	b	b	5	NULL	10	Using where; Using index; Start temporary
-1	PRIMARY	t2	ref	c	c	5	test.t1.b	1	
+1	PRIMARY	t3	index	b	b	5	NULL	10	Using where; Using index; Start temporary
+1	PRIMARY	t4	ref	c	c	5	test.t3.b	1	
 1	PRIMARY	t1	ALL	b	NULL	NULL	NULL	10	Using where; Using join buffer (flat, BNL join)
-1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	7	Using where; End temporary; Using join buffer (flat, BNL join)
+1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	8	Using where; End temporary; Using join buffer (flat, BNL join)
 SELECT a, b, d FROM t1, t2
 WHERE ( b, d ) IN
-( SELECT b, d FROM t1, t2 WHERE b = c );
+( SELECT b, d FROM t1 as t3, t2 as t4 WHERE b = c );
 a	b	d
 1	2	1
 1	2	1
@@ -2768,7 +2768,7 @@ WHERE (t1_1.a, t1_2.a) IN ( SELECT a, b FROM v1 );
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1_1	ALL	NULL	NULL	NULL	NULL	11	Using where
 1	PRIMARY	t1_2	ALL	NULL	NULL	NULL	NULL	11	
-1	PRIMARY	<derived3>	ref	key0	key0	5	test.t1_1.a	2	Using where; FirstMatch(t1_2)
+1	PRIMARY	<derived3>	ref	key0	key0	5	test.t1_1.a	1	Using where; FirstMatch(t1_2)
 3	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	11	
 SELECT * FROM t1 AS t1_1, t1 AS t1_2
 WHERE (t1_1.a, t1_2.a) IN ( SELECT a, b FROM v1 );