drop table if exists t1;
create table t1
(
key1 int not null, 
key2 int not null, 
INDEX i1(key1),
INDEX i2(key2)
) engine=innodb;
explain select * from t1 where key1 < 5 or key2 > 197;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	i1,i2	i1,i2	4,4	NULL	8	Using sort_union(i1,i2); Using where
select * from t1 where key1 < 5 or key2 > 197;
key1	key2
0	200
1	199
2	198
3	197
4	196
explain select * from t1 where key1 < 3 or key2 > 195;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	i1,i2	i1,i2	4,4	NULL	8	Using sort_union(i1,i2); Using where
select * from t1 where key1 < 3 or key2 > 195;
key1	key2
0	200
1	199
2	198
3	197
4	196
alter table t1 add str1 char (255) not null, 
add zeroval int not null default 0,
add str2 char (255) not null,
add str3 char (255) not null;
update t1 set str1='aaa', str2='bbb', str3=concat(key2, '-', key1 div 2, '_' ,if(key1 mod 2 = 0, 'a', 'A'));
alter table t1 add primary key (str1, zeroval, str2, str3);
explain select * from t1 where key1 < 5 or key2 > 197;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	i1,i2	i1,i2	4,4	NULL	8	Using sort_union(i1,i2); Using where
select * from t1 where key1 < 5 or key2 > 197;
key1	key2	str1	zeroval	str2	str3
4	196	aaa	0	bbb	196-2_a
3	197	aaa	0	bbb	197-1_A
2	198	aaa	0	bbb	198-1_a
1	199	aaa	0	bbb	199-0_A
0	200	aaa	0	bbb	200-0_a
explain select * from t1 where key1 < 3 or key2 > 195;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	i1,i2	i1,i2	4,4	NULL	8	Using sort_union(i1,i2); Using where
select * from t1 where key1 < 3 or key2 > 195;
key1	key2	str1	zeroval	str2	str3
4	196	aaa	0	bbb	196-2_a
3	197	aaa	0	bbb	197-1_A
2	198	aaa	0	bbb	198-1_a
1	199	aaa	0	bbb	199-0_A
0	200	aaa	0	bbb	200-0_a
drop table t1;