create table t1(a blob unique , b blob , c blob, unique(b,c));
insert into t1 values(1,1,1);
insert into t1 values(2,2,2),(3,3,3),(4,4,4),(5,5,5);
insert into t1 select a+5, b+5, c+5 from t1;
insert into t1 select a+10, b+10, c+10 from t1;
insert into t1 select a+20, b+20, c+20 from t1;
insert into t1 select a+40, b+40, c+40 from t1;
explain select * from t1 where a="1";;
id	1
select_type	SIMPLE
table	NULL
type	NULL
possible_keys	NULL
key	NULL
key_len	NULL
ref	NULL
rows	NULL
Extra	Impossible WHERE noticed after reading const tables
explain select * from t1 where b="34" and c = "34";;
id	1
select_type	SIMPLE
table	t1
type	ALL
possible_keys	b
key	NULL
key_len	NULL
ref	NULL
rows	80
Extra	Using where
explain select * from t1 where c="34" and b="34";;
id	1
select_type	SIMPLE
table	t1
type	ALL
possible_keys	b
key	NULL
key_len	NULL
ref	NULL
rows	80
Extra	Using where
explain select * from t1 where c="34";;
id	1
select_type	SIMPLE
table	t1
type	ALL
possible_keys	NULL
key	NULL
key_len	NULL
ref	NULL
rows	80
Extra	Using where
explain select * from t1 where b="34";;
id	1
select_type	SIMPLE
table	NULL
type	NULL
possible_keys	NULL
key	NULL
key_len	NULL
ref	NULL
rows	NULL
Extra	Impossible WHERE noticed after reading const tables
drop table t1;