IDT ifelse or case statement

Hi Guys, need advice and help

scenario

i need to show in my WEBi report items which have different items

i have purchasing doc types and PIINS

i am showing all purchasing doc types e.g A, B, C, D , E with all the piins in my reports

but for purchasing doc type  Z  i only wanna show piins that 900*.

how can i write a statement for this in IDT, cannot be in Webi.

if (PO type = z then piin= 900 else Piin)