drop table if exists t1,t2;
create table t1 (
c_id int(11) not null default '0',
org_id int(11) default null,
unique key contacts$c_id (c_id),
key contacts$org_id (org_id)
) engine=innodb;
insert into t1 values 
(2,null),(120,null),(141,null),(218,7), (128,1),
(151,2),(234,2),(236,2),(243,2),(255,2),(259,2),(232,3),(235,3),(238,3),
(246,3),(253,3),(269,3),(285,3),(291,3),(293,3),(131,4),(230,4),(231,4);
create table t2 (
slai_id int(11) not null default '0',
owner_tbl int(11) default null,
owner_id int(11) default null,
sla_id int(11) default null,
inc_web int(11) default null,
inc_email int(11) default null,
inc_chat int(11) default null,
inc_csr int(11) default null,
inc_total int(11) default null,
time_billed int(11) default null,
activedate timestamp null default null,
expiredate timestamp null default null,
state int(11) default null,
sla_set int(11) default null,
unique key t2$slai_id (slai_id),
key t2$owner_id (owner_id),
key t2$sla_id (sla_id)
) engine=innodb;
insert into t2(slai_id, owner_tbl, owner_id, sla_id) values
(1,3,1,1), (3,3,10,2), (4,3,3,6), (5,3,2,5), (6,3,8,3), (7,3,9,7),
(8,3,6,8), (9,3,4,9), (10,3,5,10), (11,3,11,11), (12,3,7,12);
flush tables;
select si.slai_id
from t1 c join t2 si on
((si.owner_tbl = 3 and si.owner_id = c.org_id) or 
( si.owner_tbl = 2 and si.owner_id = c.c_id)) 
where 
c.c_id = 218 and expiredate is null;
slai_id
12
select * from t1 where org_id is null;
c_id	org_id
2	NULL
120	NULL
141	NULL
select si.slai_id
from t1 c join t2 si on
((si.owner_tbl = 3 and si.owner_id = c.org_id) or 
( si.owner_tbl = 2 and si.owner_id = c.c_id)) 
where 
c.c_id = 218 and expiredate is null;
slai_id
12
drop table t1, t2;
create table t1m (a int) engine=myisam;
create table t1i (a int) engine=innodb;
create table t2m (a int) engine=myisam;
create table t2i (a int) engine=innodb;
insert into t2m values (5);
insert into t2i values (5);
select min(a) from t1m;
min(a)
NULL
select min(7) from t1m;
min(7)
NULL
select min(7) from DUAL;
min(7)
NULL
explain select min(7) from t2m join t1m;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
select min(7) from t2m join t1m;
min(7)
NULL
select max(a) from t1m;
max(a)
NULL
select max(7) from t1m;
max(7)
NULL
select max(7) from DUAL;
max(7)
NULL
explain select max(7) from t2m join t1m;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Select tables optimized away
select max(7) from t2m join t1m;
max(7)
NULL
select 1, min(a) from t1m where a=99;
1	min(a)
1	NULL
select 1, min(a) from t1m where 1=99;
1	min(a)
1	NULL
select 1, min(1) from t1m where a=99;
1	min(1)
1	NULL
select 1, min(1) from t1m where 1=99;
1	min(1)
1	NULL
select 1, max(a) from t1m where a=99;
1	max(a)
1	NULL
select 1, max(a) from t1m where 1=99;
1	max(a)
1	NULL
select 1, max(1) from t1m where a=99;
1	max(1)
1	NULL
select 1, max(1) from t1m where 1=99;
1	max(1)
1	NULL
select min(a) from t1i;
min(a)
NULL
select min(7) from t1i;
min(7)
NULL
select min(7) from DUAL;
min(7)
NULL
explain select min(7) from t2i join t1i;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t2i	ALL	NULL	NULL	NULL	NULL	1	
1	SIMPLE	t1i	ALL	NULL	NULL	NULL	NULL	1	
select min(7) from t2i join t1i;
min(7)
NULL
select max(a) from t1i;
max(a)
NULL
select max(7) from t1i;
max(7)
NULL
select max(7) from DUAL;
max(7)
NULL
explain select max(7) from t2i join t1i;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t2i	ALL	NULL	NULL	NULL	NULL	1	
1	SIMPLE	t1i	ALL	NULL	NULL	NULL	NULL	1	
select max(7) from t2i join t1i;
max(7)
NULL
select 1, min(a) from t1i where a=99;
1	min(a)
1	NULL
select 1, min(a) from t1i where 1=99;
1	min(a)
1	NULL
select 1, min(1) from t1i where a=99;
1	min(1)
1	NULL
select 1, min(1) from t1i where 1=99;
1	min(1)
1	NULL
select 1, max(a) from t1i where a=99;
1	max(a)
1	NULL
select 1, max(a) from t1i where 1=99;
1	max(a)
1	NULL
select 1, max(1) from t1i where a=99;
1	max(1)
1	NULL
select 1, max(1) from t1i where 1=99;
1	max(1)
1	NULL
explain select count(*), min(7), max(7) from t1m, t1i;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1m	system	NULL	NULL	NULL	NULL	0	const row not found
1	SIMPLE	t1i	ALL	NULL	NULL	NULL	NULL	1	
select count(*), min(7), max(7) from t1m, t1i;
count(*)	min(7)	max(7)
0	NULL	NULL
explain select count(*), min(7), max(7) from t1m, t2i;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1m	system	NULL	NULL	NULL	NULL	0	const row not found
1	SIMPLE	t2i	ALL	NULL	NULL	NULL	NULL	1	
select count(*), min(7), max(7) from t1m, t2i;
count(*)	min(7)	max(7)
0	NULL	NULL
explain select count(*), min(7), max(7) from t2m, t1i;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t2m	system	NULL	NULL	NULL	NULL	1	
1	SIMPLE	t1i	ALL	NULL	NULL	NULL	NULL	1	
select count(*), min(7), max(7) from t2m, t1i;
count(*)	min(7)	max(7)
0	NULL	NULL
drop table t1m, t1i, t2m, t2i;