Current_date() will only give you the date.
now() give you the datetime when the statement,procedure etc... started.
sysdate() give you the current datetime.
Look at the seconds after waiting 5 seconds between now()1 sysdate()1 with the following query (scroll to the right):
select now(),sysdate(),current_date(),sleep(5),now(),sysdate();
-- will give
-- now() sysdate() current_date() sleep(5) now()1 sysdate()1
-- 6/10/2014 2:50:04 AM 6/10/2014 2:50:04 AM 6/10/2014 12:00:00 AM 0 6/10/2014 2:50:04 AM 6/10/2014 2:50:09 AM
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