Crazy Query

 Do you have any idea how this queries are working  ?


 select * from user_details d where exists (select 1/0 from dual x where d.first_name =x.dummy) ;

 select * from user_details d where exists (select 1/0 from dual ) ;

 Query  to get HR, MI,SS
 
select trunc((sysdate-created)*24) "Hr",trunc(mod( (sysdate-created)*24*60,60)) "Mi",
 trunc( mod( (sysdate-created)*24*60*60,60 )) "Sec"
from all_users where rownum < 10 ;