drop table if exists t1;
CREATE TABLE t1 (
a char(5) NOT NULL,
b char(4) NOT NULL,
KEY (a),
KEY (b)
);
INSERT INTO t1 VALUES ('A','B'),('b','A'),('C','c'),('D','E'),('a','a');
INSERT INTO t1 VALUES 
('AA','BB'),('bb','AA'),('CC','cc'),('DD','EE'),('aa','aa');
INSERT INTO t1 VALUES 
('AAA','BBB'),('bbb','AAA'),('CCC','ccc'),('DDD','EEE'),('aaa','aaa');
select * from t1,t1 as t2
where length(t1.A)=1 and length(t2.B)=1 ;
a	b	a	b
A	B	A	B
b	A	A	B
C	c	A	B
D	E	A	B
a	a	A	B
A	B	b	A
b	A	b	A
C	c	b	A
D	E	b	A
a	a	b	A
A	B	C	c
b	A	C	c
C	c	C	c
D	E	C	c
a	a	C	c
A	B	D	E
b	A	D	E
C	c	D	E
D	E	D	E
a	a	D	E
A	B	a	a
b	A	a	a
C	c	a	a
D	E	a	a
a	a	a	a
explain select t1.*,t2.* from t1,t1 as t2
where t1.A=t2.B and length(t1.A)=1 and length(t2.B)=1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	a	NULL	NULL	NULL	15	Using where
1	SIMPLE	t2	ref	b	b	4	test.t1.a	1	Using where
select t1.*,t2.* from t1,t1 as t2
where t1.A=t2.B and length(t1.A)=1 and length(t2.B)=1
order by binary t1.a,t2.a;
a	b	a	b
A	B	a	a
A	B	b	A
C	c	C	c
a	a	a	a
a	a	b	A
b	A	A	B
select * from t1 where a='a';
a	b
A	B
a	a
drop table t1;