drop table if exists  t0,t1,t2;
select count(*) from t1;
count(*)
64801
explain select key1,key2 from t1 where key1=100 and key2=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2	key1,key2	5,5	NULL	58	Using intersect(key1,key2); Using where; Using index
select key1,key2 from t1 where key1=100 and key2=100;
key1	key2
100	100
explain select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key1,key2,key3,key4	5,5,5,5	NULL	154	Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
key1	key2	key3	key4	filler1
100	100	100	100	key1-key2-key3-key4
insert into t1 (key1, key2, key3, key4, filler1) values (100, 100, -1, -1, 'key1-key2');
insert into t1 (key1, key2, key3, key4, filler1) values (-1, -1, 100, 100, 'key4-key3');
explain select key1,key2,filler1 from t1 where key1=100 and key2=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2	key1,key2	5,5	NULL	58	Using intersect(key1,key2); Using where
select key1,key2,filler1 from t1 where key1=100 and key2=100;
key1	key2	filler1
100	100	key1-key2-key3-key4
100	100	key1-key2
explain select key1,key2 from t1 where key1=100 and key2=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2	key1,key2	5,5	NULL	58	Using intersect(key1,key2); Using where; Using index
select key1,key2 from t1 where key1=100 and key2=100;
key1	key2
100	100
100	100
explain select key1,key2,key3,key4 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key1,key2,key3,key4	5,5,5,5	NULL	154	Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select key1,key2,key3,key4 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
key1	key2	key3	key4
100	100	100	100
100	100	-1	-1
-1	-1	100	100
explain select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key1,key2,key3,key4	5,5,5,5	NULL	154	Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
key1	key2	key3	key4	filler1
100	100	100	100	key1-key2-key3-key4
100	100	-1	-1	key1-key2
-1	-1	100	100	key4-key3
explain select key1,key2,key3 from t1 where key1=100 and key2=100 and key3=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3	key1,key2,key3	5,5,5	NULL	2	Using intersect(key1,key2,key3); Using where; Using index
select key1,key2,key3 from t1 where key1=100 and key2=100 and key3=100;
key1	key2	key3
100	100	100
insert into t1 (key1,key2,key3,key4,filler1) values (101,101,101,101, 'key1234-101');
explain select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=101;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3	key1,key2,key3	5,5,5	NULL	83	Using union(intersect(key1,key2),key3); Using where
select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=101;
key1	key2	key3	key4	filler1
100	100	100	100	key1-key2-key3-key4
100	100	-1	-1	key1-key2
101	101	101	101	key1234-101
select key1,key2, filler1 from t1 where key1=100 and key2=100;
key1	key2	filler1
100	100	key1-key2-key3-key4
100	100	key1-key2
update t1 set filler1='to be deleted' where key1=100 and key2=100;
update t1 set key1=200,key2=200 where key1=100 and key2=100;
delete from t1 where key1=200 and key2=200;
select key1,key2,filler1 from t1 where key2=100 and key2=200;
key1	key2	filler1
explain select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key1,key2,key3,key4	5,5,5,5	NULL	152	Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
key1	key2	key3	key4	filler1
-1	-1	100	100	key4-key3
delete from t1 where key3=100 and key4=100;
explain select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key1,key2,key3,key4	5,5,5,5	NULL	152	Using union(intersect(key1,key2),intersect(key3,key4)); Using where
select key1,key2,key3,key4,filler1 from t1 where key1=100 and key2=100 or key3=100 and key4=100;
key1	key2	key3	key4	filler1
explain select key1,key2 from t1 where key1=100 and key2=100;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2	key1,key2	5,5	NULL	57	Using intersect(key1,key2); Using where; Using index
select key1,key2 from t1 where key1=100 and key2=100;
key1	key2
insert into t1 (key1, key2, key3, key4, filler1) values (100, 100, 200, 200,'key1-key2-key3-key4-1');
insert into t1 (key1, key2, key3, key4, filler1) values (100, 100, 200, 200,'key1-key2-key3-key4-2');
insert into t1 (key1, key2, key3, key4, filler1) values (100, 100, 200, 200,'key1-key2-key3-key4-3');
explain select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key3,key1,key2,key4	5,5,5,5	NULL	136	Using union(key3,intersect(key1,key2),key4); Using where
select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
key1	key2	key3	key4	filler1
100	100	200	200	key1-key2-key3-key4-3
100	100	200	200	key1-key2-key3-key4-2
100	100	200	200	key1-key2-key3-key4-1
insert into t1 (key1, key2, key3, key4, filler1) values (-1, -1, -1, 200,'key4');
explain select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key3,key1,key2,key4	5,5,5,5	NULL	146	Using union(key3,intersect(key1,key2),key4); Using where
select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
key1	key2	key3	key4	filler1
100	100	200	200	key1-key2-key3-key4-3
100	100	200	200	key1-key2-key3-key4-2
100	100	200	200	key1-key2-key3-key4-1
-1	-1	-1	200	key4
insert into t1 (key1, key2, key3, key4, filler1) values (-1, -1, 200, -1,'key3');
explain select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	key1,key2,key3,key4	key3,key1,key2,key4	5,5,5,5	NULL	156	Using union(key3,intersect(key1,key2),key4); Using where
select key1,key2,key3,key4,filler1 from t1 where key3=200 or (key1=100 and key2=100) or key4=200;
key1	key2	key3	key4	filler1
100	100	200	200	key1-key2-key3-key4-3
100	100	200	200	key1-key2-key3-key4-2
100	100	200	200	key1-key2-key3-key4-1
-1	-1	-1	200	key4
-1	-1	200	-1	key3
explain select * from t1 where st_a=1 and st_b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	st_a,st_b	4,4	NULL	2637	Using intersect(st_a,st_b); Using where
explain select st_a,st_b from t1 where st_a=1 and st_b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	st_a,st_b	4,4	NULL	2637	Using intersect(st_a,st_b); Using where; Using index
explain select st_a from t1 ignore index (st_a) where st_a=1 and st_b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,stb_swt1a_2b,stb_swt1b,st_b	st_b	4	const	15093	Using where
explain select * from t1 where st_a=1 and swt1a=1 and swt2a=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a	sta_swt21a	12	const,const,const	971	
explain select * from t1 where st_b=1 and swt1b=1 and swt2b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	stb_swt1a_2b,stb_swt1b,st_b	stb_swt1a_2b	8	const,const	3879	Using where
explain select * from t1 where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	sta_swt12a,stb_swt1a_2b	12,12	NULL	44	Using intersect(sta_swt12a,stb_swt1a_2b); Using where
explain select * from t1 ignore index (sta_swt21a, stb_swt1a_2b) 
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,st_a,stb_swt1b,st_b	sta_swt12a,stb_swt1b	12,8	NULL	44	Using intersect(sta_swt12a,stb_swt1b); Using where
explain select * from t1 ignore index (sta_swt21a, sta_swt12a, stb_swt1a_2b) 
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt1a,sta_swt2a,st_a,stb_swt1b,st_b	sta_swt1a,sta_swt2a,stb_swt1b	8,8,8	NULL	43	Using intersect(sta_swt1a,sta_swt2a,stb_swt1b); Using where
explain select * from t1 ignore index (sta_swt21a, sta_swt12a, stb_swt1a_2b, stb_swt1b) 
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1 and swt2b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt1a,sta_swt2a,st_a,st_b	sta_swt1a,sta_swt2a,st_b	8,8,4	NULL	168	Using intersect(sta_swt1a,sta_swt2a,st_b); Using where
explain select * from t1 
where st_a=1 and swt1a=1 and swt2a=1 and st_b=1 and swt1b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	sta_swt12a,stb_swt1a_2b	12,12	NULL	44	Using intersect(sta_swt12a,stb_swt1a_2b); Using where
explain select * from t1 
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	sta_swt1a,stb_swt1b	8,8	NULL	174	Using intersect(sta_swt1a,stb_swt1b); Using where
explain select st_a from t1 
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	sta_swt1a,stb_swt1b	8,8	NULL	174	Using intersect(sta_swt1a,stb_swt1b); Using where; Using index
explain select st_a from t1 
where st_a=1 and swt1a=1 and st_b=1 and swt1b=1 and swt1b=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index_merge	sta_swt12a,sta_swt1a,sta_swt2a,sta_swt21a,st_a,stb_swt1a_2b,stb_swt1b,st_b	sta_swt1a,stb_swt1b	8,8	NULL	174	Using intersect(sta_swt1a,stb_swt1b); Using where; Using index
drop table t0,t1;
create table t2 (
a char(10),
b char(10),
filler1 char(255),
filler2 char(255),
key(a(5)),
key(b(5))
);
select count(a) from t2 where a='BBBBBBBB';
count(a)
4
select count(a) from t2 where b='BBBBBBBB';
count(a)
4
expla_or_bin select count(a_or_b) from t2 where a_or_b='AAAAAAAA' a_or_bnd a_or_b='AAAAAAAA';
id	select_type	ta_or_ba_or_ble	type	possia_or_ble_keys	key	key_len	ref	rows	Extra_or_b
1	SIMPLE	t2	ref	a_or_b,a_or_b	a_or_b	6	const	4	Using where
select count(a) from t2 where a='AAAAAAAA' and b='AAAAAAAA';
count(a)
4
select count(a) from t2 ignore index(a,b) where a='AAAAAAAA' and b='AAAAAAAA';
count(a)
4
insert into t2 values ('ab', 'ab', 'uh', 'oh');
explain select a from t2 where a='ab';
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t2	ref	a	a	6	const	1	Using where
drop table t2;
CREATE TABLE t1(c1 INT, c2 INT DEFAULT 0, c3 CHAR(255) DEFAULT '',
KEY(c1), KEY(c2), KEY(c3));
INSERT INTO t1(c1) VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),
(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0),(0);
INSERT INTO t1 VALUES(0,0,0);
CREATE TABLE t2(c1 int);
INSERT INTO t2 VALUES(1);
DELETE t1 FROM t1,t2 WHERE t1.c1=0 AND t1.c2=0;
SELECT * FROM t1;
c1	c2	c3
DROP TABLE t1,t2;
