SAP query. Retrieve values basing on input on selection screen - abap

Question

I am stuck with coding a SAP query..I am new to ABAP.
What I would like to achieve is a join between tables ESLL, EKPO, EKKO.
Specifically these are the steps I would like to achieve:
in the selection parameter every time I will enter the query I will
give a different value for ESLL-EXTSRVNO;
basing on that value the query automatically should select ESLL-PACKNO basing on ESLL-EXTSRVNO given;
then the query should put ESLL-SUB_PACKNO equal
to the ESLL-PACKNO values of the steps before;
then the query should
put the new ESLL-PACKNO values equal to EKPO-PACKNO and retrieve the
following fields: EKPO-EBELN, EKPO-EBELP, EKPO-MATKL.
I have already written some code inside the infoset, but I do not know how to fix it.
In the "data" section I have written:
DATA: it_esll TYPE TABLE OF esll.
DATA: it_esll2 TYPE TABLE OF esll.
DATA: it_ekpo TYPE TABLE OF ekpo.
In the "start-of-selection" section I have written:
SELECT packno
FROM esll
INTO TABLE it_esll.
IF sy-subrc EQ 0.
SELECT packno FROM esll
into TABLE it_esll2
for ALL ENTRIES IN it_esll
where sub_packno EQ it_esll-packno.
IF sy-subrc EQ 0.
SELECT ebeln ebelp bukrs werks matkl menge netpr peinh
FROM ekpo
into TABLE it_ekpo
for ALL ENTRIES IN it_esll2
WHERE packno EQ it_esll2-packno.
endif.
endif.
And, in order to display all the information I want, I have put the following joins:
ESLL-PACKNO --> EKPO-PACKNO --> EKPO-EBELN --> EKKO-EBELN
At then end I would like to display these information:
EKPO-EBELN
EKPO-EBELP
EKPO-MATKL
EKKO-BSART
EKPO-PACKNO
Could you please help me?

Answer 1

One option could be to use Alias table in your infoset, something like this:
First table: ESLL;
Second table ZESLL (Alias on ESLL) with join ZESLL-PACKNO = ESLL-SUB_PACKNO;
Third table: EKPO with join on EKPO-PACKNO = ZESLL-PACKNO;
Fourth table: EKKO with join on EBELN;
So you can avoid ABAP
Infoset Join