I am trying to make my report so that when the user opens it they are prompted for both the ID number and surname, but are told to only enter one. The formula for the select expert should then be able to check which value is null and then filter records by the parameter that isnt. Before now I have only programmed in java but I gave it a go and this is what I have so far.

if ({clientmaster.SURNAME} = "") then
{clientmaster.ID} = {?Client ID}
else if isnull({clientmaster.ID}) = true
then {clientmaster.SURNAME} = {?SURNAME}

Any help you can give would be appreciated, thank you.