sql server 2008 - How to subtract today's date (current date) from delivery date SQL Query? -

i have table has current date , delivery date. want minus due date current date , want save days left in dbtable

select clientid,         curentdate,         deliverydate datediff(day,-(deliverydate) current_timestamp) days_left  dbo.tblorder 

e.g:

• today date 12/1/2014
• delivery date 20/1/2014
• days left 8

did in the documentation examples on how use datediff?

select clientid, currentdate, deliverydate,    days_left = datediff(day, current_timestamp, deliverydate)  dbo.tblorder;