Deleting a Material BOM 
You delete BOMs in change mode. You can only delete
one specific BOM at a time. You can only delete one alternative of a multiple BOM or one variant of a variant BOM. You can delete a BOM with or without history.
Deleting without history
The selected BOM is deleted online. Once the delete transaction is updated, you can create a new BOM with the same Material/Plant/Usage.
Deleting with history
If you delete the BOM with reference to a change number, the system takes the valid-from data from the change master record as the deletion date. The BOM is deleted on this date.
Valid-from date of the change number
You can only use a change number with a valid-from date within the validity period of the BOM.
Example 1:
BOM MAT is created with the valid-from date 05/01/1997. You want to delete the BOM with change number D1 . The change master record has the valid-from date
01/01/1997 . You cannot delete the BOM with change number D1 , because the BOM is not valid on 01/01/1997.
Example 2:
BOM MAT is created with the valid-from date 05/01/1997 . You want to delete the BOM with change number D2 . The change master record has the valid-from date 06/01/1997 . The BOM is deleted on 06/01/1997 . The state of the BOM before the change ( 05/01/1997 to 05/31/1997 ) is retained. This means you can still process the BOM within this validity period.
Checking the BOM item
Before you can delete a bill of material, the system checks the BOM items as follows:
- Items with object dependencies
If a configurable bill of material contains one or more items with object dependencies, its change number must support dependency maintenance. The change number cannot be valid as of a date in the past.
- Items with operation allocation
If one or more items are allocated to an operation, you see a warning message.
因为我做的是CHANGE WITH HISTORY...这大概就是CHANGE CODE 的作用. I finally understand.