For different sourcetypes you can use eval name = coalesce(field1, field2)
and combining different field names to single field you use the above mentioned by Takajian eval name = mvappend(field1, field2, ...)
it can combine multiple fields to single.
eval command is useful to combine filed. Can you try following command and confirm if this work for your case?
... | eval same_name=mvappend(field1, field2)