descriptor.getVisibleFieldCount(),
unionOutputSymbols.size());
int unionFieldId = 0;
for (Field field : descriptor.getVisibleFields()) {
int fieldIndex = descriptor.indexOf(field);
symbolMapping.put(unionOutputSymbols.get(unionFieldId), childOutputSymobls.get(fieldIndex));
unionFieldId++;
}
sources.add(relationPlan.getRoot());