The following lines contain the word 'select', 'insert', 'update' or 'delete':
SELECT 1
INTO dummy
FROM sys.DUAL
WHERE not exists (SELECT 1
FROM po_rfq_vendors
WHERE po_header_id = X_po_header_id
AND vendor_id = X_vendor_id
AND vendor_site_id = X_vendor_site_id
AND ((X_rowid is null) or
(X_rowid != rowid)));