Error while extending iSupply Portal VO

Question

I try to extending iSupply Portal PosPosummaryVO by create a new view object, and extend PosPosummaryVO. after sql statement step, I appear a error message
" Each row in the Query Result Columns must be mapped to a uniqe Query Attribute in the Mapped Entity columns."
What does it mean?
I only add a where condidtion in the sql
the sql is
select 'Select_flag' as Select_flag, --> orginal is 'Select_flag', an error occure say it was a key word or existing attr., so I add an as alias
poh.po_num,
poh.comments,
poh.creation_date,
poh.po_release_id,
to_char(null) agent_name,
poh.currency_code,
to_char(0) as amount,
poh.ACCEPTANCE_DUE_DATE,
poh.vendor_id,
poh.po_header_id,
poh.agent_id,
poh.type_lookup_code,
poh.type_name,
poh.vendor_contact_id,
poh.vendor_site_id,
poh.acceptance_required_flag,
poh.approved_date,
poh.revision_num,
to_char(null) PO_STATUS_CODE ,
to_char(null) PO_STATUS_DISP ,
poh.org_name,
poh.attribute1,
poh.attribute2,
poh.attribute3,
poh.attribute4,
poh.attribute5,
poh.attribute6,
poh.attribute7,
poh.attribute8,
poh.attribute9,
poh.attribute10,
poh.attribute11,
poh.attribute12,
poh.attribute13,
poh.attribute14,
poh.attribute15,
poh.attribute_category,
decode(poh.po_release_id,null,'PosHdrAttach','PosRelAttach')
as SwitchAttach,
'N' as retrieve_flag,
poh.CANCEL_FLAG,
poh.CLOSED_CODE,
poh.FROZEN_FLAG,
poh.USER_HOLD_FLAG,
poh.global_agreement_flag,
to_char(null) consigned_consumption_flag,
poh.vendor_name,
poh.vendor_site_code,
poh.po_release_id po_release_id2,
poh.vendor_number ,
poh.vendor_id vendor_id2, org_id,
poh.segment1,
poh.release_num,
to_char(null) business_document_type,
to_char(null) business_document_id,
to_char(null) business_document_version,
0 as ship_to_location_id,
security_level_code,
access_level_code
from pos_view_po_summary_v poh
where poh.type_lookup_code = 'standard' ---> new where condition

Answer 1

Here is the workaround
1. while extending give the query as select 'X' from dual; and finish the extenstion...
2. Right click on the extended VO and select Edit
3. Now paste the original query and Apply the changes
4. Check the attribute mappings as well and correct it..
5. compare the original VO attributes and extended VO attributes. If you find any differences correct it.
--Prasanna