I am a SAP SD consultant and recently faced with two new terms, mass order change and ALV , I also need to know about the transaction code.

There is transaction MASS which can be used to carry out mass changes in the sales order and other objects.

Mass Maintenance: (Use to change multiple fields in multiple documents at the same time).  I have done mass change for customers; and orders should work the same way too.

1) Try t-code [MASS] and select sales orders & execute

2) Choose the table or tables for your selection criteria and also for fields you want to change.
Then execute. (suppose your selection criteria fields are from "sales order header data" table and the field you want to change, is in "item data" table)

3) Put in the sales documents(21000000, 21000001) you want to change and also the items(10) you want to change.
- click on " choose selection fields" button
- From the Pool, move the fields you want to the "select fields" using arrows.

4)From mass maintenace menu, click on "Enter new field values"
-click on "sales order item data" tab and choose the field you want to change.
(for example. I want to change plant for item 10)
-enter the new value (of the plant to be)
-click on "Adopt" and execute

5)In "sales order item data" tab, you see the new value of the plant you entered at the top and the old values of item 10 are below.
-click on "change field values" button.  you see all the old values are changed to new values.
-save
Note:  it will take some time depending on how many records you have.
Check:  Go to [SM37] and see the status of the job you are running and once finished, export the spool file to a spreadsheet.
Before you do mass maintenance, go to the particular table in [se16] and get the results.  Then do the mass maintenance and compare the results with this one.  If they match, then you are good to go.

Note:  If you have any user exits that affect the results, ask them to deactivate the MODCHECKS still you are done with mass maintenance & activate them again.

Is there a way to change the billing date on a ton of sales orders with same old billing date to a same new billing date?

This can be done using the mass transaction:
Transaction: MASS 
Object Type: BUS2032 
Tables: SD Document: Business item data 
Sel Field: Billing Date (MASSSDHE and MASSSDPO) 
- Or you can just select by document numbers (May be more efficient) 
Execute - List will be provide for changes 

Sel Chg Fld: Billing Date 
Set new billing date value in the New Values field 
Click on lower billing date column 
Click on Carry out a Mass Change button 
Click on Save button 

Suggestion is to test this on a few orders in your development system to get a feel on how this works before applying this to any production data. MASS is a very powerful tool. 

I have 100000 sales orders whith an incorrect price and I would like to do a massive condition update with pricing type "B" (Carry out new pricing). Is there a transaction or program for this? 

Go to VA05 execute the report. Select all sales orders you want to update the price, Go to the Menu EDIT --> MASS Change ---> New Pricing. System will display all the re-pricing options. Select B. It will re-price all the sales orders. 

You can try for one or two order initially check the results and if it is OK, then you can do for others.

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