SQL Transaction Type Check

I am trying to produce a report showing certain transactions allocated to a particular incident.  In one particular case I need to check if a particular incident has one of two specific transaction types, if it does then it should use one of them, but never both. Is there a clean way of doing this.  The only way I can think of is using subqueries/table aliases and coalesce to get the result.  I would still need the other transaction types included if they had been entered.


Many thanks

Damian