create table t1(a int primary key , b int , c int, index(b,c));
insert into t1 values(1,1,1),(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;
 --query_vertical explain select * from t1 where a=34;
 --query_vertical explain select * from t1 where b=34 and c = 34;
 --query_vertical explain select * from t1 where c=34;
drop table t1;