def set_field_tables(self):
		if len(self.tables) > 1:
			for i, f in enumerate(self.fields):
				if '.' not in f:
					self.fields[i] = '{0}.{1}'.format(self.tables[0], f)
If there are more than one table, the fieldname must not be ambigous.
dataset/ETHPy150Open frappe/frappe/frappe/model/db_query.py/DatabaseQuery.set_field_tables