Enhance the performance of FM!

Question

Hi,
I have a FM which is using  inner Join statement from four DB tables for extracting selected fields into an Internal table as shown below:
select ofield1 pfield2 tfield3 cfield4
( and so on upto approximately 30 fileds )
into 
(Itab-filed1, itab-field2, itab-field3, itab-field4, and so on ) from
DB1 as o inner join
DB2  as p on 0field1 = Pfield1 left join
DB3 as c on pfield2 = cfield2 and
                   Pfield3 = cfield3  left join
DB4  as t on pfield4 = tField4
        and  pfield5 = tfield5
where conditions----
Since the Join statements are really decreasing the performance, task now is to increase the performance by removing select and end select.
Any ideas?
Raj

Answer 1

*Code to demonstrate select command
*Code to demonstrate select into internal table command
TYPES: BEGIN OF t_bkpf,
include structure bkpf.
  bukrs LIKE bkpf-bukrs,
  belnr LIKE bkpf-belnr,
  gjahr LIKE bkpf-gjahr,
  bldat LIKE bkpf-bldat,
  monat LIKE bkpf-monat,
  budat LIKE bkpf-budat,
  xblnr LIKE bkpf-xblnr,
  awtyp LIKE bkpf-awtyp,
  awkey LIKE bkpf-awkey,
END OF t_bkpf.
DATA: it_bkpf TYPE STANDARD TABLE OF t_bkpf INITIAL SIZE 0,
      wa_bkpf TYPE t_bkpf.
TYPES: BEGIN OF t_bseg,
*include structure bseg.
  bukrs     LIKE bseg-bukrs,
  belnr     LIKE bseg-belnr,
  gjahr     LIKE bseg-gjahr,
  buzei     LIKE bseg-buzei,
  mwskz     LIKE bseg-mwskz,         "Tax code
  umsks     LIKE bseg-umsks,         "Special G/L transaction type
  prctr     LIKE bseg-prctr,         "Profit Centre
  hkont     LIKE bseg-hkont,         "G/L account
  xauto     LIKE bseg-xauto,
  koart     LIKE bseg-koart,
  dmbtr     LIKE bseg-dmbtr,
  mwart     LIKE bseg-mwart,
  hwbas     LIKE bseg-hwbas,
  aufnr     LIKE bseg-aufnr,
  projk     LIKE bseg-projk,
  shkzg     LIKE bseg-shkzg,
  kokrs     LIKE bseg-kokrs,
END OF t_bseg.
DATA: it_bseg TYPE STANDARD TABLE OF t_bseg INITIAL SIZE 0,
      wa_bseg TYPE t_bseg.
*Select directly into an internal table
SELECT bukrs belnr gjahr buzei mwskz umsks prctr hkont xauto koart
       dmbtr mwart hwbas aufnr projk shkzg kokrs
  FROM bseg
  INTO TABLE it_bseg.
Select directly into an internal table where fields are in a
different order or not all fields are specified
SELECT bukrs belnr gjahr buzei mwskz umsks prctr hkont xauto koart
       dmbtr mwart hwbas aufnr projk shkzg kokrs
  FROM bseg
  INTO CORRESPONDING FIELDS OF TABLE it_bseg.
*Select... endselect command
SELECT bukrs belnr gjahr buzei mwskz umsks prctr hkont xauto koart
       dmbtr mwart hwbas aufnr projk shkzg kokrs
  FROM bseg
  INTO wa_bseg.
  APPEND wa_bseg TO it_bseg.
ENDSELECT.
*Select FOR ALL ENTRIES command
SELECT bukrs belnr gjahr bldat monat budat xblnr awtyp awkey
  UP TO 100 ROWS
  FROM bkpf
  INTO TABLE it_bkpf.
IF sy-subrc EQ 0.
The FOR ALL ENTRIES comand only retrieves data which matches
entries within a particular internal table.
  SELECT bukrs belnr gjahr buzei mwskz umsks prctr hkont xauto koart
         dmbtr mwart hwbas aufnr projk shkzg kokrs
    FROM bseg
    INTO TABLE it_bseg
    FOR ALL ENTRIES IN it_bkpf
    WHERE bukrs EQ it_bkpf-bukrs AND
          belnr EQ it_bkpf-belnr AND
          gjahr EQ it_bkpf-gjahr.
ENDIF.