Excluding values in expressions

[#1]

Hello everyone, I have an issue that I am trying to solve.  I have been working with qlikview for about a year and a half now.  What I am trying to achieve is an expression that will exclude all Part #'s that have not been sold.  I am trying to link the part # through the SO Due Date as a null pretty much, SO something like if(SO_MAST.DueDate=0,where(SO_MAST.DueDate >='10/1/2015') and(Part #....... etc. etc.  Honestly I have a very slight idea on how to format this expression to make it work the way I need, can someone please help me?

[sunny_talwar]

Not sure I understand this if statement

if(SO_MAST.DueDate=0,where(SO_MAST.DueDate >='10/1/2015')

Can you may be elaborate a little?

[#3]

Honestly I don't know if the example I gave is correct.  What I'm trying to do is get a list of part #'s that are not linked to due dates in the past year by excluding part #'s that are linked to due dates.  I hope this helps