How to move one column from one internal table to another using VALUE/BASE/FOR?

[bmierzwi]

Hello,
I have an internal table storing some of the customer's data and I want to append a column from another table which stores e-mail addresses. LIFNR is the common field between tables.
I have the function itself already working:

LOOP AT gt_email_addr INTO gwa_email_addr.
      LOOP AT gt_main INTO gwa_main.
        IF gwa_main-lifnr = gwa_email_addr-lifnr.
          gwa_main-smtp_addr = gwa_email_addr-smtp_addr.
          MODIFY gt_main FROM gwa_main.
        ENDIF.
      ENDLOOP.
ENDLOOP.

BUT I would prefer it to work as a FOR loop. At the moment I am trying something like this:

gt_main = VALUE #( BASE gt_main FOR wa IN gt_email_addr ( CORRESPONDING #( wa ) ) ).

But it doesn't work - the line above actually just appends a new record to gt_main. The documentation seems to be very "tip-of-the-iceberg" about it and provides just some theory and all other sources explain how I can use such a loop to add literal values provided within the code instead and I can't find anything about moving data from one table to another in this way.
Of course, I also tried different versions of that statement, e.g. using WHERE clause (trying to connect those LIFNRs), but, apparently, wa has no such field.

Any ideas what I am doing wrong? It kind of feels like I "just" need to approach the BASE part differently, but nothing seems to work.

Kind Regards,
Bartosz

[Sandra_Rossi]

You should use Constructor Expressions only to construct values once (construct = "initialize values from scratch"), not construct again just to mimic an update, it will be simply counter-performing.

If you can Construct only once, at a specific place, if you have all data sources available, then you can use VALUE/FOR and any constructor expression you need.

[bmierzwi]

Hey,

Thanks for the answer. Do I understand correctly then than my current solution (LOOP within a LOOP) is the correct way to go if I want move data from a single column of an internal table to another internal table?

And that my attempts at optimization should in fact be used only if I want to create a new table?

Kind Regards,

[Sandra_Rossi]

rule-of-thumb:

• To update existing data: don't use Constructor Expressions which rebuild from scratch
• To initialize a variable the first time: prefer using Constructor Expressions if it's legible

[lenapadeken]

"The documentation seems to be very "tip-of-the-iceberg" about it and provides just some theory" - really? The documentation provides you with two examples which suit your use case:

https://help.sap.com/doc/abapdocu_latest_index_htm/latest/en-US/index.htm?file=abenfor_in_itab.htm

Best regards,

Lena

[bmierzwi]

Hey,

Thank you for the answer and sorry for the late reply.

I've been trying with these, but I really couldn't see how the presented examples fit my use-case. It feels like they're solving a different problem, albeit I suppose this can be attributed to me still being a junior in SAP.

I will analyse it deeper.

Kind Regards,
Bartek