How can I do it optimally ?

From: <luba_at_usb>
Date: Fri, 19 Jan 2001 10:33:31 +0200
Message-ID: <949c74$1ng$1@news.ukrsotsbank.com>

How can I do it optimally ?
update Tab1
set Tab1.field2=(

     select  sum (decode (field1,1,field2,0)+decode (field1,2,field3,0))
     from Tab1 where field1 in (1,2))

where field1=1 ; Received on Fri Jan 19 2001 - 02:33:31 CST