Decode function

[bang_dba]

Hi,
Can i use two column names in a single decode function...

for eg
select sum(decode(A.TableA,20,B.TableB,0)) .....

I was analyzing a query just similar to above select stmt. Was just wondering why they have used two columns in one decode function...

can somebody put some light on this...

[TomazZ]

It does sum(value) where value is defined as:
if A.TableA = 20 then value=B.TableB
else value=0