This will show your current username, user_id, account status, lock_date, and Expiry_date. Simple but really handy if you are going on vacation soon and do not want your account to lock out while you are away.
Select * from user_users
Oracle has a great table that will give you some great meta data about your other tables and columns called “all_tab_cols“.
select Table_name, Column_name,Data_type,High_value,low_value from all_tab_cols order by table_name desc