You can use a second table OCCURRENCE from the same transactions TABLE. This is often called a "self join".
The portal references a table ocurrence. Thus you can still use the portal as you wish, but is will be based on "Tansactions2" rather than "Transactions"
Is this what you're looking for?
Thanks Ninja. That worked. I love fields that show only related values and it is working very well now. Are you new to the forum? I haven't come across you before.