provider_id, from the source
t0Medicare Outpatient Charges table with records from the
t1Medicare Inpatient Charges table, we create a comparison that joins records when table's
provider_ids are equal.
t1, the variables in that table will be available to keep in the output table or discard using the variable selector interface, prefixed with a
t1tag. You can also access these variables when filtering rows, creating new variables, etc.