set analysis expression

[smilingjohn]

Hi All, 

I need to write  set analysis expression something like the below described in a language format. 

Count of Tickets for severity =2  if  createdDate is less than MediumDate and ( ShippedDate should be greater than  MediumDate  OR  ShippedDate is null) 

I am trying to write this in set exoression but i am facing issues for or OR condition is please help 

count({<SEVERITy={'2' }>}if(createdDate <MediumDate and isnull(ShippedDate ) or ShippedDate >=MediumDate ,Ticket))

the above expression is taking overall OR between CreatedDate and ShippedDate 

Thanks in Advance 

[Digvijay_Singh]

If possible create few flags after comparing dates in the script if the dates are in the same table and use something like this - 

Count({

<Severity={2},HigherMediumDate={1},HigherShipDateFlag={1}> +

(<Severity={2},HigherMediumDate={1},ShipDateNullflag={1}>

}Ticket)