SCN上有個帖子，說明了one-time vendor的概念，現轉載在此，以作學習。
http://forums.sdn.sap.com/thread.jspa?messageID=8154128&tstart=0#8154128
T-code：XK01， the same to normal vendor.
You can create special vendor master records for vendors from whom you procure goods only once or rarely, so-called One-Time Vendor Master Records.
For example, suppose you order goods from a vendor with whom you usually do not place orders, because your main vendor was not able to supply the required items. In this case, you would use a "one-time vendor" master record.
In contrast to other master records, a "one-time vendor" master record is used for several vendors. The purpose of this is to avoid the unnecessary creation of an excessive number of individual vendor master records. For this reason, you may not store any vendor-specific data in a "one-time vendor" master record.
When creating a "one-time vendor" master record, you must assign a one-time account group. This account group determines that the vendor-specific fields are suppressed. You don’t need to enter this data until the time a purchasing document (e.g. a PO) is created.
When you create a purchasing document with a one-time vendor, you will be asked to enter the vendor address. Enter the vendor’s name and address.
Like all other master records, you can display, block, or delete one-time vendor master records.