Explain the Delete process : Mr Halo

[badrinathn]

I am a bit confused the way the delete statements work.
For egs :

1) delete from account ;
2) delete from account a
where account_number in
(select distinct account_number from another_table);

3) delete from account a
where a.account_number = (select .account_number
from another_table b
where a.account_number = b.account_number)

Please clarify
Badrinath