Performance for validating data against various database tables

Question

My Problem:

I "loop" over a table into a local structure named ls_eban..

and with those information I must follow these instructions:

1. ls_eban-matnr MUST BE in table zmd_scmi_st01 ( 1. control Table (global) )
2. ls_eban-werks MUST BE in table zmd_scmi_st05 ( 2. control Table (global) )
3. ls_eban-knttp MUST BE in table zmd_scmi_st06 ( 3. control Table (global) )

I need a selection that is clear and performant. I actually have one, but it isn't performant at all.

My solution:

SELECT st01~matnr st05~werks st06~knttp
  FROM       zmd_scmi_st01 AS st01
  INNER JOIN zmd_scmi_st05 AS st05
  ON         st05~werks = ls_eban-werks
  INNER JOIN zmd_scmi_st06 AS st06
  ON         knttp = ls_eban-knttp
INTO TABLE   lt_control
WHERE        st01~matnr = ls_eban-matnr AND st01~bedarf = 'X'
  AND        st05~bedarf = 'X'.

I also have to say, that the control tables doesn't have any relation with each other (no primary key and no secondary key).

Answer 1

The first thing you should not do is have the select inside the loop. Instead of

loop at lt_eban into ls_eban.
      Select ....
endloop.

You should do a single select.

if lt_eban[] is not initial.
   select ...
     into table ...
     from ...
      for all entries in lt_eban
    where ...
endif.

There may be more inefficiencies to be corrected if we had more info ( as mentioned in the comment by vwegert. For instance, really no keys on the control tables? ) but the select in a loop is the first thing that jumps out at me.