The main patch for WL#24:

"index_merge: fair choice between index_merge union and range access"

mysql-test/include/world.inc:
  A new include file to upload the world database.
mysql-test/include/world_schema.inc:
  A new include file to create tables of the world database.
mysql-test/r/index_merge_myisam.result:
  The results for test cases testing the optimizations added in WL#24 for MyISAM.
mysql-test/r/range_vs_index_merge.result:
  The results for test cases testing the optimizations added in WL#24 for InnoDB.
mysql-test/t/range_vs_index_merge.test:
  Test cases to test the optimizations added in WL#24 for MyISAM.
mysql-test/t/range_vs_index_merge_innodb.test:
  Test cases to test the optimizations added in WL#24 for InnoDB.
sql/sql_list.h:
  Fixed a bug that did not allow adding a non-empty list to an empty list.

mysql-test/include/world_schema.inc

+CREATE TABLE Country (
+  Code char(3) NOT NULL default '',
+  Name char(52) NOT NULL default '',
+  SurfaceArea float(10,2) NOT NULL default '0.00',
+  Population int(11) NOT NULL default '0',
+  Capital int(11) default NULL,
+  PRIMARY KEY  (Code),
+  UNIQUE INDEX (Name)
+);
+CREATE TABLE City (
+  ID int(11) NOT NULL auto_increment,
+  Name char(35) NOT NULL default '',
+  Country char(3) NOT NULL default '',
+  Population int(11) NOT NULL default '0',
+  PRIMARY KEY  (ID),
+  INDEX (Population),
+  INDEX (Country) 
+);
+CREATE TABLE CountryLanguage (
+  Country char(3) NOT NULL default '',
+  Language char(30) NOT NULL default '',
+  Percentage float(3,1) NOT NULL default '0.0',
+  PRIMARY KEY  (Country, Language),
+  INDEX (Percentage)
+);

mysql-test/r/index_merge_myisam.result

@@ -115,11 +115,11 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 explain select * from t0 where
 (key1 < 3 or key2 < 3) and (key3 < 100);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t0	range	i1,i2,i3	i3	4	NULL	95	Using where
+1	SIMPLE	t0	index_merge	i1,i2,i3	i1,i2	4,4	NULL	6	Using sort_union(i1,i2); Using where
 explain select * from t0 where
 (key1 < 3 or key2 < 3) and (key3 < 1000);
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t0	ALL	i1,i2,i3	NULL	NULL	NULL	1024	Using where
+1	SIMPLE	t0	index_merge	i1,i2,i3	i1,i2	4,4	NULL	6	Using sort_union(i1,i2); Using where
 explain select * from t0 where
 ((key1 < 4 or key2 < 4) and (key2 <5 or key3 < 4))
 or
@@ -259,7 +259,7 @@ explain
 select * from t0,t1 where (t0.key1=t1.key1) and
 (t0.key1=3 or t0.key2=4) and t1.key1<200;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t0	ALL	i1,i2	NULL	NULL	NULL	1024	Using where
+1	SIMPLE	t0	index_merge	i1,i2	i1,i2	4,4	NULL	2	Using union(i1,i2); Using where
 1	SIMPLE	t1	ref	i1	i1	4	test.t0.key1	1	
 explain
 select * from t0,t1 where (t0.key1=t1.key1) and

mysql-test/t/range_vs_index_merge_innodb.test

+--source include/have_innodb.inc
+
+SET SESSION STORAGE_ENGINE='InnoDB';
+
+--source t/range_vs_index_merge.test
+
+SET SESSION STORAGE_ENGINE=DEFAULT;

sql/sql_list.h

@@ -168,6 +168,14 @@ public:
   {
     if (!list->is_empty())
     {
+#if 0
+#else
+      if (is_empty())
+      {
+        *this= *list;
+        return;
+      }
+#endif
       *last= list->first;
       last= list->last;
       elements+= list->elements;