Perofrmance issue on data fetch from db table

Dear Experts,
I have one requirement which explained below step wise.
Step - 1 : I have a parameter on selection screen from where i ll get my ebeln value (User Input field) and that ebeln i ll check in ekpo table for validations.
              If valid i  keep it in a variable gw_ebeln.
Step - 2 : Need to fetch lifnr fron ekko based on gw_ebeln value.
Step - 3 : Need to fetch adrnr from lfa1 based on lifnr (Previously fetched from ekko table in step 2)
Step - 4 : Need to fetch email field from adr6 table based on adrnr value (Previously fetched from lfa1 table in step 3)
Step - 5 : Now for these mail id , I need to send mail by given fm.
My question is : I can create structure for step 2 , step 3, step 4 and by using " for all entries " in select statement i ll fetch my mail id in step 4.
So instead of creating structure and then use for all entries , I can fetch by using "select single" statement for step 2 , step3 step 4.bcz i am fetching only one field from all 3 table.
So which one is better performance wise and why ?
I need more and clear clarifications on these difference.
Please provide me suggestions.
Thanks & Regards,
Ajit Sarangi

Hi Ajit,
We are referring item table EKPO. Multiple entries are possible.
To append the values in final internal table, we are going to process the LOOP. Inside loop, we should not use the Select statement, that decreases the performance. Database Interaction process should not done inside Loop...Endloop.
That's why we are creating the Internal table for processing the values. Since we need limited number of fields in the particular table, we are creating our own structure in the program.
For this case, For all entries will give better performance with compare to Select Single.
Rajkumar Narsimman

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    The following diagram is an example of how this might happen:
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    2. The dispatcher receives the request to execute a dialog step from user 2 and directs it to work process 1, which is now free again. The work process executes the dialog step as in step 1.
    3. While work process 1 is still working, the dispatcher receives a further request from user 1 and directs it to work process 2, which is free.
    4. After work processes 1 and 2 have finished processing their dialog steps, the dispatcher receives another request from user 1 and directs it to work process 1, which is free again.
    5. While work process 1 is still working, the dispatcher receives a further request from user 2 and directs it to work process 2, which is free.
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    • A work process can execute dialog steps of different programs from different users.
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