Performance Tuning :: Sql_id And Sql_child_id Are Not Null For SQL Statement

i am trying to analyze a query i have and noticed that it does not show the sql_id in v$session.

preparing a test case:

create table t1(a number, b varchar(10));
insert into t1 values(123 , 'value1');

when i execute

select count(*) from dual;
select * from dual;
select count(*) from t1;

i can see the sql_id by running

select
sql_id sql_id_,
sql_child_number sql_child_num,
module module_,
action action_,
logon_time lgtime,

[code]....

however, when i'm running

select * from t1

sql_id and sql_child_id in v$session appears to be null, and i can't analyze it.

why those columns are NULL?