set echo on

execute dbms_random.seed(0);

drop table t1
/

create table t1 as
select
	rownum as id,
	trunc(7100 * dbms_random.normal) as normal, -- normal distribution of data
	trunc(dbms_random.value(0,50000)) as uniform -- uniform distribution of data
from
	all_objects a,all_objects b
where
	rownum <= 1000000
/

create index idx_1 on t1(normal,uniform)
/

execute dbms_stats.gather_table_stats(user,'T1');

explain plan 
for
select id
from t1
where normal = 42
and uniform = 42
/

@show_plan_9i

drop index idx_1
/

create index idx_1 on t1(normal,uniform)
/

execute dbms_stats.gather_table_stats(user,'T1');

explain plan 
for
select id
from t1
where normal = 42
and uniform = 42
/

@show_plan_9i