Ability to aggregate based on selected attributes in data exchange

Summary:

The client wants to aggregate all transactions into 1 row for a specific attribute. Is there a way to do this in data exchange?

Content (please ensure you mask any confidential information):

Currently we are using SQL mappings to filter data that gets loaded into each transaction matching group. We are also using SQL mappings to flip signs in the data. We would still need to filter these and flip signs, but we want the data aggregated based on one specific attribute. My thoughts were to bring in source only attributes, but I cannot figure out a way to use these in SQL mappings since they are not considered dimensions in data exchange. If someone could point me in the direction to use source attributes in SQL mappings if there is no