Lets discuss some good practices of coding

This blog will help folks who just on-boarded for ABAP in understanding the codes in line with it.

Note: 1st block of code indicates incorrect way of coding. Codes that follow the golden rules are written just after that.

1. Having small result sets

1.1 WHERE condition

Requirement: Fetch customers whose customer type is ‘B’.

DATA : lv_id TYPE scustom-id,
       lv_name TYPE scustom-name,
       lv_discount TYPE scustom-discount,
       lv_custtype TYPE scustom-custtype.

• Bad Practice

SELECT id name discount custtype FROM scustom
INTO (lv_id, lv_name, lv_discount, lv_custtype).
IF lv_custtype = 'B'.
WRITE : / lv_id, lv_name, lv_discount, lv_custtype.
ENDIF.
ENDSELECT.

• Good Practice

TYPES: BEGIN OF ty_scustom,
id       TYPE S_CUSTOMER,
name     TYPE S_CUSTNAME,
discount TYPE S_DISCOUNT,
custtype TYPE S_CUSTTYPE,
       END OF ty_scustom.

DATA: it_scuctom TYPE TABLE OF ty_scustom,
      wa_scustom TYPE ty_scustom.

SELECT id name discount custtype FROM scustom
INTO TABLE it_scustom   
WHERE custtype = 'B'.
LOOP AT it_scustom INTO wa_scustom.
WRITE : / wa_scustom-id, wa_scustom-name, 
          wa_scustom-discount, wa_scustom-custtype.
ENDLOOP.

Reason: Fetching filtered data is better than fetching the entire data set and then filtering it.

1.2 HAVING clause

Requirement: Fetch details of flights having the minimum seat occupancy. The minimum seat occupancy should be greater than zero.

DATA: lv_sflight TYPE sflight,
      lv_min     TYPE sflight-seatsocc.

• Bad Practice

SELECT carrid connid MIN( seatsocc ) FROM sflight
INTO (lv_sflight-carrid, lv_sflight-connid, lv_min)
GROUP BY carrid connid.
IF lv_min > 0.
WRITE:/ lv_sflight-carrid, lv_sflight-connid, lv_min.
ENDIF.
ENDSELECT.

• Good Practice

TYPES: BEGIN OF ty_sflight,
carrid   TYPE S_CARR_ID,
connid   TYPE S_CONN_ID,
seatsocc TYPE S_SEATSOCC,
       END OF ty_sflight.

DATA: it_sflight TYPE TABLE OF ty_sflight,
      wa_sflight TYPE ty_sflight.

SELECT carrid connid MIN( seatsocc ) FROM sflight
INTO TABLE it_sflight
GROUP BY carrid connid 
HAVING MIN( seatsocc ) > 0.
LOOP AT it_sflight INTO wa_sflight.
WRITE:/ wa_sflight-carrid, wa_sflight-connid, wa_sflight-min_socc.
END LOOP.

Reason: Do the calculation in the select query itself

1.3 Transferring required rows

Requirement: Fetch details

DATA: lt_scustom TYPE TABLE OF scustom,
      lw_scustom TYPE scustom.

• Bad Practice

SELECT id name discount custtype FROM scustom
INTO CORRESPONDING FIELDS OF TABLE lt_scustom
WHERE country = 'DE'.
DELETE lt_scustom WHERE custtype = 'P'.
LOOP AT lt_scustom INTO lw_scustom.
WRITE: / lw_scustom -id, lw_scustom -name, 
         lw_scustom-discount, lw_scustom -custtype.
ENDLOOP.

• Good Practice

SELECT id name discount custtype FROM scustom
INTO CORRESPONDING FIELDS OF TABLE lt_scustom
WHERE country = 'DE' AND custtype <> 'P'.
LOOP AT lt_scustom INTO lw_scustom.
WRITE: / lw_scustom-id, lw_scustom-name, 
         lw_scustom-discount, lw_scustom-custtype.
ENDLOOP.

Reason: Fetching required rows is better than fetching the entire data set and then delete the unwanted rows

2. Having small transferred data sets

2.1 DISTINCT clause

Requirement: Fetch distinct details of customers who avail discounts

DATA : lt_scustom TYPE TABLE OF scustom,
       lw_scustom TYPE scustom.

• Bad Practice

SELECT custtype discount FROM scustom
INTO CORRESPONDING FIELDS OF TABLE lt_scustom
WHERE discount > 0
ORDER BY custtype discount DESCENDING.
DELETE ADJACENT DUPLICATES FROM lt_scustom.
LOOP AT lt_scustom INTO lw_scustom.
WRITE : / lw_scustom-id, lw_scustom-discount.
ENDLOOP.

• Good Practice

SELECT DISTINCT custtype discount FROM scustom 
INTO CORRESPONDING FIELDS OF TABLE lt_scustom
WHERE discount > 0
ORDER BY custtype discount DESCENDING.
LOOP AT lt_scustom INTO lw_scustom.
WRITE : / lw_scustom-id, lw_scustom-discount.
ENDLOOP.

2.2 Using aggregate functions

Requirement: Display the total number of seats reserved in an airline in any given year

DATA : lv_sum      TYPE sflight-seatsocc,
       lv_seatsocc TYPE sflight-seatsocc.

• Bad Practice

SELECT seatsocc FROM sflight 
INTO lv_seatsocc
WHERE carrid = 'LH'AND fldate LIKE '2013 %'.
lv_sum = lv_sum + lv_seatsocc.
ENDSELECT.
WRITE : / lv_sum.

• Good Practice

SELECT SUM( seatsocc )FROM sflight 
INTO lv_sum
WHERE carrid = 'LH'AND fldate LIKE '2013 %'.
WRITE : / lv_sum.

2.3 Changing only required columns

Requirement: Change the connection number of a specific flight

DATA : lw_book TYPE sbook.

• Bad Practice

SELECT * FROM sbook
INTO lw_book
WHERE carrid = 'LH'AND connid = '0400'AND fldate >= '20160101'.
lw_book-connid = '0500'.
UPDATE sbook FROM lw_book.ENDSELECT.

• Good Practice

UPDATE sbookSET connid ='0500'
WHERE carrid = 'LH' AND connid = '0400' AND fldate >= '20160101'.

3. Reducing number of queries

3.1 Using set operations instead of individual operations

Requirement: Insert a record into the table SBOOK

• Bad Practice

LOOP AT it_sbook INTO lw_sbook.
INSERT INTO sbook VALUES lw_sbook.
ENDLOOP.

• Good Practice

INSERT sbook FROM TABLE lt_sbook.

3.2 Avoiding multiple accesses

Requirement: Delete details of flights with carrier ID AA and connection ID 17

• Bad Practice

SELECT SINGLE * FROM sflight
INTO lv_sflight WHERE carrid = 'AA' AND connid = '0017'.
IF sy-subrc EQ 0.
DELETE FROM sflight WHERE carrid = 'AA' AND connid = '0017'.
IF sy-subrc EQ 0.
COMMIT WORK.
ENDIF.
ENDIF.

• Good Practice

DELETE FROM sflight 
WHERE carrid = 'AA' AND connid = '0017'.
IF sy-subrc EQ 0.
COMMIT WORK.
ENDIF.

Reason: Delete data in the repository directly instead of fetching the dataset and then deleting it

3.3 Avoiding SELECT inside LOOPs

Requirement: Fetch details

• Bad Practice

LOOP AT lt_sflight INTO lw_sflight.
SELECT SINGLE bookid customid FROM sbook
INTO lw_sbook
WHERE carrid = lv_sflight-carrid AND connid = lv_sflight-connid
AND fldate = lv_sflight-fldate.
WRITE : / lv_sflight-carrid, lv_sflight-connid, lv_sflight-fldate,
          lv_sbook-bookid, lv_sbook-customid.
ENDLOOP.

• Good Practice

IF lt_sflight IS NOT INITIAL.
SELECT SINGLE bookid customid FROM sbook
INTO CORRESPONDING FIELDS OF TABLE lt_sbook
FOR ALL ENTRIES IN lt_sflight
WHERE carrid = lv_sflight-carrid AND connid = lv_sflight-connid
  AND fldate = lv_sflight-fldate.
ENDIF.