If I create sub-section and select "Merge into existing section", those columns will append with the parent fields. How can I do if I would like to keep parent record even when there is no record in sub-section?

It seems that the parent will not show if there is no sub-section record merged.

Staff Response: 

Yes, at the moment missing merged records will cause the whole row not not appear. This may be changed in the future so it's configurable in the section. In the meantime to fix this you can add a Script Source under the subsections. The script source would just read:

if Count(&path/SubFormName)=0 then
    return new record for &path/SubFormName
else
   return load(&path/SubFormName)
end if 

...replace SubFormName with the name of the subform. That should be enough to make it create an empty subform if there's no data, putting in blank entries in the report instead of omitting the entire row.

Thanks.