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
table	type	possible_keys	key	key_len	ref	rows	Extra
t1	ALL	a	NULL	NULL	NULL	5	
t2	ALL	b	NULL	NULL	NULL	5	where used
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
a	b
A	B
a	a