BUG#17314: Can't use index_merge/intersection for MERGE tables

1. Fix index access costs for MERGE tables, set block_size=myisam_block_size/#underlying_tables 
   instead of 0 which it was before.
2. Make index scans on MERGE table to return records in (key_tuple, merge_table_rowid) order, 
   instead of just (key_tuple) order. This makes an index scan on MERGE table to be truly a ROR-scan
   which is a requirement for index_merge union/intersection.


myisammrg/myrg_queue.c:
  BUG#17314: Make index scans on MERGE table return records ordered by (keytuple, merge_table_rowid).
mysql-test/r/index_merge.result:
  Testcase for BUG#17314
mysql-test/r/merge.result:
  BUG#17314: update testcase result
mysql-test/t/index_merge.test:
  Testcase for BUG#17314
sql/ha_myisammrg.cc:
  BUG#17314: For MERGE tables, set handler::block_size to myisam_block_size/#underlying_tables, and not to 0.

1 files changed, 22 insertions, 0 deletions

diff --git a/mysql-test/r/index_merge.result b/mysql-test/r/index_merge.result
index db87253e19a..3a69f56cbd3 100644
--- a/mysql-test/r/index_merge.result
+++ b/mysql-test/r/index_merge.result
@@ -402,3 +402,25 @@ explain select * from t1 force index(cola,colb) WHERE cola = 'foo' AND colb = 'b
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	index_merge	cola,colb	cola,colb	3,3	NULL	24	Using intersect(cola,colb); Using where
 drop table t1;
+create table t0 (a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t1 (
+a int, b int, 
+filler1 char(200), filler2 char(200),
+key(a),key(b)
+);
+insert into t1 select @v:= A.a, @v, 't1', 'filler2' from t0 A, t0 B, t0 C;
+create table t2 like t1;
+create table t3 (
+a int, b int, 
+filler1 char(200), filler2 char(200),
+key(a),key(b)
+) engine=merge union=(t1,t2);
+explain select * from t1 where a=1 and b=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	index_merge	a,b	a,b	5,5	NULL	#	Using intersect(a,b); Using where
+explain select * from t3 where a=1 and b=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t3	index_merge	a,b	a,b	5,5	NULL	#	Using intersect(a,b); Using where
+drop table t3;
+drop table t0, t1, t2;