drop table if exists t1,t2;
create table t1 (a int, b int not null,unique key (a,b),index(b)) type=myisam;
insert ignore into t1 values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(null,7),(9,9),(8,8),(7,7),(null,9),(null,9),(6,6);
explain select * from t1 where a is null;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a	a	5	const	3	Using where; Using index
explain select * from t1 where a is null and b = 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	9	const,const	1	Using where; Using index
explain select * from t1 where a is null and b = 7;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	9	const,const	1	Using where; Using index
explain select * from t1 where a=2 and b = 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	const	a,b	a	9	const,const	1	
explain select * from t1 where a<=>b limit 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index	NULL	a	9	NULL	12	Using where; Using index
explain select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a,b	a	9	NULL	3	Using where; Using index
explain select * from t1 where (a is null or a = 7) and b=7;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	b	4	const	2	Using where
explain select * from t1 where (a is null and b>a) or a is null and b=7 limit 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where; Using index
explain select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a,b	a	9	NULL	2	Using where; Using index
explain select * from t1 where a > 1 and a < 3 limit 1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a	a	5	NULL	1	Using where; Using index
explain select * from t1 where a > 8 and a < 9;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a	a	5	NULL	1	Using where; Using index
select * from t1 where a is null;
a	b
NULL	7
NULL	9
NULL	9
select * from t1 where a is null and b = 7;
a	b
NULL	7
select * from t1 where a<=>b limit 2;
a	b
1	1
2	2
select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
a	b
1	1
2	2
select * from t1 where (a is null or a > 0 and a < 3) and b > 7 limit 3;
a	b
NULL	9
NULL	9
select * from t1 where (a is null or a = 7) and b=7;
a	b
NULL	7
7	7
select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
a	b
NULL	7
NULL	9
NULL	9
alter table t1 modify b blob not null, add c int not null, drop key a, add unique key (a,b(20),c), drop key b, add key (b(10));
explain select * from t1 where a is null and b = 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where
explain select * from t1 where a is null and b = 2 and c=0;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where
explain select * from t1 where a is null and b = 7 and c=0;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where
explain select * from t1 where a=2 and b = 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	1	Using where
explain select * from t1 where a<=>b limit 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	12	Using where
explain select * from t1 where (a is null or a > 0 and a < 3) and b < 5 and c=0 limit 3;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a,b	a	5	NULL	5	Using where
explain select * from t1 where (a is null or a = 7) and b=7 and c=0;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	a,b	NULL	NULL	NULL	12	Using where
explain select * from t1 where (a is null and b>a) or a is null and b=7 limit 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where
explain select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	a,b	a	5	const	3	Using where
explain select * from t1 where a > 1 and a < 3 limit 1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a	a	5	NULL	1	Using where
explain select * from t1 where a is null and b=7 or a > 1 and a < 3 limit 1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a,b	a	5	NULL	4	Using where
explain select * from t1 where a > 8 and a < 9;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	a	a	5	NULL	1	Using where
explain select * from t1 where b like "6%";
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	b	b	12	NULL	1	Using where
select * from t1 where a is null;
a	b	c
NULL	7	0
NULL	9	0
NULL	9	0
select * from t1 where a is null and b = 7 and c=0;
a	b	c
NULL	7	0
select * from t1 where a<=>b limit 2;
a	b	c
1	1	0
2	2	0
select * from t1 where (a is null or a > 0 and a < 3) and b < 5 limit 3;
a	b	c
1	1	0
2	2	0
select * from t1 where (a is null or a > 0 and a < 3) and b > 7 limit 3;
a	b	c
NULL	9	0
NULL	9	0
select * from t1 where (a is null or a = 7) and b=7 and c=0;
a	b	c
NULL	7	0
7	7	0
select * from t1 where a is null and b=9 or a is null and b=7 limit 3;
a	b	c
NULL	7	0
NULL	9	0
NULL	9	0
select * from t1 where b like "6%";
a	b	c
6	6	0
drop table t1;
CREATE TABLE t1 (
id int(10) unsigned NOT NULL auto_increment,
uniq_id int(10) unsigned default NULL,
PRIMARY KEY  (id),
UNIQUE KEY idx1 (uniq_id)
) TYPE=MyISAM;
CREATE TABLE t2 (
id int(10) unsigned NOT NULL auto_increment,
uniq_id int(10) unsigned default NULL,
PRIMARY KEY  (id)
) TYPE=MyISAM;
INSERT INTO t1 VALUES (1,NULL),(2,NULL),(3,1),(4,2),(5,NULL),(6,NULL),(7,3),(8,4),(9,NULL),(10,NULL);
INSERT INTO t2 VALUES (1,NULL),(2,NULL),(3,1),(4,2),(5,NULL),(6,NULL),(7,3),(8,4),(9,NULL),(10,NULL);
explain select id from t1 where uniq_id is null;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ref	idx1	idx1	5	const	1	Using where
explain select id from t1 where uniq_id =1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	const	idx1	idx1	5	const	1	
UPDATE t1 SET id=id+100 where uniq_id is null;
UPDATE t2 SET id=id+100 where uniq_id is null;
select id from t1 where uniq_id is null;
id
101
102
105
106
109
110
select id from t2 where uniq_id is null;
id
101
102
105
106
109
110
DELETE FROM t1 WHERE uniq_id IS NULL;
DELETE FROM t2 WHERE uniq_id IS NULL;
SELECT * FROM t1 ORDER BY uniq_id, id;
id	uniq_id
3	1
4	2
7	3
8	4
SELECT * FROM t2 ORDER BY uniq_id, id;
id	uniq_id
3	1
4	2
7	3
8	4
DROP table t1,t2;
CREATE TABLE `t1` (
`order_id` char(32) NOT NULL default '',
`product_id` char(32) NOT NULL default '',
`product_type` int(11) NOT NULL default '0',
PRIMARY KEY  (`order_id`,`product_id`,`product_type`)
) TYPE=MyISAM;
CREATE TABLE `t2` (
`order_id` char(32) NOT NULL default '',
`product_id` char(32) NOT NULL default '',
`product_type` int(11) NOT NULL default '0',
PRIMARY KEY  (`order_id`,`product_id`,`product_type`)
) TYPE=MyISAM;
INSERT INTO t1 (order_id, product_id, product_type) VALUES
('3d7ce39b5d4b3e3d22aaafe9b633de51',1206029, 3),
('3d7ce39b5d4b3e3d22aaafe9b633de51',5880836, 3),
('9d9aad7764b5b2c53004348ef8d34500',2315652, 3);
INSERT INTO t2 (order_id, product_id, product_type) VALUES
('9d9aad7764b5b2c53004348ef8d34500',2315652, 3);
select t1.* from t1
left join t2 using(order_id, product_id, product_type)
where t2.order_id=NULL;
order_id	product_id	product_type
select t1.* from t1
left join t2 using(order_id, product_id, product_type)
where t2.order_id is NULL;
order_id	product_id	product_type
3d7ce39b5d4b3e3d22aaafe9b633de51	1206029	3
3d7ce39b5d4b3e3d22aaafe9b633de51	5880836	3
drop table t1,t2;
create table t1 (id int);
insert into t1 values (null), (0);
create table t2 (id int);
insert into t2 values (null);
select * from t1, t2 where t1.id = t2.id;
id	id
alter table t1 add key id (id);
select * from t1, t2 where t1.id = t2.id;
id	id
drop table t1,t2;
create table t1 (
id  integer,
id2 integer not null,
index (id),
index (id2)
);
insert into t1 values(null,null),(1,1);
Warnings:
Warning	1261	Data truncated, NULL supplied to NOT NULL column 'id2' at row 1
select * from t1;
id	id2
NULL	0
1	1
select * from t1 where id <=> null;
id	id2
NULL	0
select * from t1 where id <=> null or id > 0;
id	id2
NULL	0
1	1
select * from t1 where id is null or id > 0;
id	id2
NULL	0
1	1
select * from t1 where id2 <=> null or id2 > 0;
id	id2
1	1
select * from t1 where id2 is null or id2 > 0;
id	id2
1	1
delete from t1 where id <=> NULL;
select * from t1;
id	id2
1	1
drop table t1;