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Efficient ABAP/4 Coding Techniques




OBJECTIVE

In this chapter we are going to learn efficient coding Techniques in

ABAP/4. The following topics are covered.

Processing Database tables

Processing internal tables Miscellaneous

String Manipulation




1 Processing Database Tables

1.1 Readin g thro ugh a set of related tables

When reading through a set of related tables, use a logical database

whenever possible. The combination of defining a logical database (a

program that reads a table and its dependant table entries) and using the

logical database-related event keywords (e.g. GET) is more efficient thana set of nested SELECT ... ENDSELECT statements.

1.2 Check ing SELECT-OPTIONS when readin g v ia a Logical Database

When using the GET event keyword to retrieve records via a logicaldatabase, selection can be restricted by using the CHECK statement

(using either CHECK select-opt ion(s) or CHECK condi t ion ).




In this case, a CHECK statement that returns a negative result terminates

the processing of GET events for subordinate database tables and the

associated data is not read. For efficiency reasons, you should therefore

always perform the CHECK at the highest possible level of the database

hierarchy.

For example:

SELECT-OPTIONS: S_CNTRY FOR KNA1-LAND1,S_COY FOR KNB1-BUKRS.

...

GET KNA1.

CHECK S_CNTRY.

GET KNB1.CHECK S_COY.

...




is more efficient than:

SELECT-OPTIONS: S_CNTRY FOR KNA1-LAND1,

S_COY FOR KNB1-BUKRS.

...

GET KNB1.

CHECK SELECT-OPTIONS. (or CHECK: S_CNTRY,

... S_COY.)

1.3 SELECT SINGLE vs. SELECT *

SELECT SINGLE * is more efficient than SELECT * … ENDSELECT.

Whenever the full key of a table is known, use:

SELECT SINGLE * FROM dbtab WHERE …. (full key).




rather than:

SELECT db_field1 db_field2 db_field3 FROM dbtabWHERE …. (full key).

...

ENDSELECT.

UP TO 1 ROW can be used to retrieve one record when the full key is

not known.

Whenever the full key is not known you will need to use the SELECT *

... ENDSELECT version of the SELECT statement.

In this case, specifying values for as many of the table’s key fields in aWHERE clause will make the SELECT statement more efficient than

checking values after the select.




1.4 Selectin g via non-key fields or non-key partial fields

When selecting records from a database table when only part of a field(on which selection is based) is known, use the LIKE option as part of

the WHERE clause.

For example:

SELECT * FROM T001GWHERE BUKRS EQ ‘US01’ AND TXTKO LIKE ‘__PERS%’.

....ENDSELECT.


SELECT * FROM T001GWHERE BUKRS EQ ‘US01’.

CHECK T001G-TXTKO+2(4) = ‘PERS’. ....

ENDSELECT.




1.5 SELECT <field1>, <field2> …

If you only need a few fields of a table, it is much more efficient to onlyretrieve exactly those fields from the database than to select all of them

(SELECT * …).

Example: if you only need the fields order number, order type and

customer from the sales document table, code as follows:

SELECT VBELN AUART KUNNR FROM VBAK

INTO (VBAK-VBELN, VBAK-AUART, VBAK-KUNNR)

WHERE …

WRITE: / …

ENDSELECT.

See the editor help for all the variants of the INTO clause.




1.6 SELECT … UP TO n ROWS

If you only need a certain number of records specify this in your select-

statement:

SELECT … FROM … UP TO 10 ROWS.

This is much faster than issuing a SELECT without the UP TO clause and

then checking for the system variable SY-DBCNT.

1.7 SELECT INTO TABLE

Reading an internal table is faster than reading a database table.

Therefore, use internal tables to store information that must be accessed

multiple times throughout a program.

Also, use internal tables when you have to read a header - item structure

for which you would otherwise use nested SELECTs

Instead of processing a

SELECT … INTO <itab-fields>

APPEND ITAB

ENDSELECT




statement it is far more efficient to select the fields straight into the

internal table and process the data from the internal table:

SELECT … FROM … INTO TABLE ITAB WHERE … LOOP AT ITAB.

… ENDLOOP.

1.8 SELECT FROM … ORDER BY

In most cases it is preferable to do the sorting within the ABAP programinstead of on the database server, that means: fill the internal table via a

SELECT statement and then sort via the SORT statement instead of

coding a SELECT … ORDER BY. The sorting of large amounts of data on

the database server affects the performance of all users on the system,

whereas the sorting within the ABAP program ‘only’ affects theapplication server. However, if an index exists on the table that can be

used for the sorting then the SELECT … ORDER BY doesn’t cause any

undue strains on the system.




1.9 Agg regate Func t ions

Instead of using ABAP, some calculations can be done by using

aggregate functions for the SELECT. These are: SUM, AVG, MIN and MAX.

Example:

SELECT MATNR SUM( KWMENG ) MEINS FROM VBAP INTO TABLE

T_VBAP WHERE … GROUP BY MATNR MEINS

This example will select the cumulative sales quantities grouped by

material number and quantity unit.

1.10 SELECT with ou t WHERE

Coding a SELECT statement without a WHERE condition is only allowedfor very small tables (e.g. customizing settings). For all other tables this

is not permitted as performance problems will occur within a short period

of time.




1.11 UPDATE

Instead of updating records within a SELECT … ENDSELECT construct

e.g. SELECT * FROM ZVBAK WHERE VBELN IN S_VBELN.

ZVBAK-VKBUR = W_VKBUR.

UPDATE ZVBAK.

ENDSELECT.

define your record selection in the UPDATE statement.

UPDATE ZVBAK SET VKBUR = W_VKBUR WHERE VBELN IN

S_VBELN. 1.12 DELETE

The same consideration as for the UPDATE is true for the DELETE:

Instead of deleting records within a SELECT … ENDSELECT construct

e.g. SELECT * FROM ZVBAK WHERE VBELN IN S_VBELN.

DELETE ZVBAK.

ENDSELECT.




define your record selection in the DELETE statement.

DELETE FROM ZVBAK WHERE VBELN IN S_VBELN.

1.13 COMMIT

ABAP reports that issue INSERT, UPDATE or DELETE commands have to

issue COMMIT WORK statements after a logical unit of work iscompleted. Missing COMMITs can lead to bottlenecks on the database

side because the system has to keep track of the table changes via

rollback segments (in order to enable a rollback of all changes since the

last commit). Rollback segments are kept in memory and missing

COMMITs can lead to overflows of the rollback segment areas. Also the

database system holds locks on the changed records that are not

released until COMMIT time.




2. Processing Internal Tables

2.1 Fill in g

To load an internal table from a database table where the structure of the

internal table is at least as wide as the structure of the database table

use:

SELECT * FROM dbtab INTO TABLE i tab.

rather than:

SELECT * FROM dbtab .

MOVE dbtab TO i tab .

APPEND i tab.

ENDSELECT.To fill an internal table without creating duplicate entries and add up the

Packed, Integer, and Floating Point fields at the same time, use:

COLLECT i tab.




2.2 Sequential Reads

If you are reading through an internal table sequentially using the LOOP

at i tab ... ENDLOOP method, but are only interested in certain entries,use a WHERE clause and specify a condition for selection. Note that the

performance of a LOOP AT ... WHERE statement is improved greatly if all

fields being compared in the WHERE clause are of the same data type.

Therefore, you should try defining the ‘compare’ fields as follows:

DATA: compare_f ie ld LIKE i tab-field1.

BEGIN OF i tab OCCURS 100,

f ield1 (5), f ield2( 5),

END OF i tab.

compare_field = <value to c ompare >.

LOOP AT i tab WHERE f ield1 = compare_f ie ld .

...

ENDLOOP.




2.3 Direc t Reads

If you are not processing the entire internal table, use:

READ TABLE i tab WITH KEY key BINARY SEARCH.

rather than:

READ TABLE i tab WITH KEY key

The second method performs a sequential read from the first record untilif finds a match.

The first method performs a binary search to find a matching record, but

the table must be sorted first.




2.4 Sortin g

Wherever possible, identify the fields to be sorted. The format:

SORT i tab BY f ield1 field2 .


SORT i tab .

SORT i tab without fields specified attempts to sort the table by all fields

other than Packed, Integer, and Floating Point fields.

2.5 Coun ting Entr ies

To count up the number of entries in an internal table, use:

DESCRIBE TABLE i tab LINES f ield .

where f ield is a work field of type ‘I’ (integer).




rather than:

LOOP AT i tab .

W_COUNT = W_COUNT + 1.ENDLOOP.

2.6 Readin g large internal tables

If you have to retrieve selected records from a large internal table, keep

this table sorted.

In this way, you can access the table via the

READ TABLE T_VBAK WITH KEY VBELN = W_VBELN BINARY SEARCH

statement.

If you only want to verify the existence of a record but don’t need any of

the fields from the record then use the additionTRANSPORTING NO FIELDS

If you only need a few fields from the internal table for processing then

use the addition

TRANSPORTING <field1> <field2> …




2.7 Moving data from internal table 1 to in ternal table 2

If you need to move all entries from one internal table to another one

which has the same structure you can simply do it via the followingstatement:

ITAB2[] = ITAB1[].

2.8 Append ing data from internal table 1 to internal table 2 If you need to append records from one internal table to another one

which has the same structure you can simply do it via the following

statement:

APPEND LINES OF ITAB1 TO ITAB2.




2.9 Loop ing at internal tables

If you are looping at an internal table just to count the number of records

that fulfill certain criteria then use the following variant of the loopstatement:

LOOP AT T_VBAK TRANSPORTING NO FIELDS WHERE …

ADD 1 TO COUNTER.

ENDLOOP.

The same applies if you only want to verify that at least one record exists

that satisfies a certain condition:

LOOP AT T_VBAK TRANSPORTING NO FIELDS WHERE …

EXIT.ENDLOOP.

IF SY-SUBRC = 0.

* Record found …

ENDIF.




2.10 DELETING DATA FROM INTERNAL TABLES

If you need to delete a subset of records from an internal table use the

following:

DELETE T_VBAK WHERE …

2.11 DELETING DUPL ICATE ENTRIES FROM AN INTERNAL TABLE

To delete duplicate entries from an internal table the table has to be

sorted by the fields used in the comparing condition. If there is no

comparing condition the table should be sorted by all fields.

DELETE ADJACENT DUPLICATES FROM T_VBAK [COMPARING field1field2 …]




3 Miscellaneous

3.1 Moving data from one table work area/struc ture to anoth er one with

an ident ical stru cture.

Use:

MOVE structure1 TO structure2 .

rather than:

MOVE-CORRESPONDING structure1 TO structure2 .

3.2 Determining the length of a str ing.

Use:

f ie ld length = STRLEN( f ield ).rather than:

IF f ield CP ‘#’.

ENDIF.

f ie ld length = SY-FDPOS.




3.3 ASSIGN statement

If assigning the contants of a field belonging to a Dictionary defined

table/data structure which itself contains a name of a field to a field

symbol, use the ASSIGN TABLE FIELD syntax of the ASSIGN statement.

For example:

ASSIGN TABLE FIELD (KNA1-NAME1) TO <fs >.


ASSIGN (KNA1-NAME1) TO <FS>.

This is because the search for the field (in this case KNA1-NAME1) is

carried out only in the Data Dictionary and not in the symbol table. The

field must then be a component field of a database table declared with the

TABLES statement. This improves the performance of this statement

considerably. In contrast to the second method above, the performance

does not depend on the number of fields used within the program.




3.4 Testi ng fo r Init ial Value

The use of the IF statement for checking whether a field is empty (i.e.

equal to the initial value for its data type) can be made more efficient bycomparing the field with another of the same data type.

For example:

IF MARA-IDNRA = SPACE.

....ENDIF.


IF MARA-IDNRA IS INITIAL.

....ENDIF.




3.5 Testing one field fo r mult ip le values

When testing an individual field for multiple values, you can use:

IF f ield = value1 .....

ELSEIF f ield = value2. ....

ENDIF.

or:CASE f ield .

WHEN value1.

....

WHEN value2 .

....WHEN value3 .

....

WHEN valuen .

....

ENDCASE.




The first method is more efficient when checking a field for up to about

five values. But the improved readability of the program code associated

with the CASE statement dictates that its use should be applied for levels

of three or greater.

3.6 Optim izing IF and CASE stru ctu res

To optimize IF and CASE structures, always test values in order of the

likelihood of each value occuring.

For example, f ieldx can have values ‘A’, ‘B’, or ‘C’. A value of ‘B’ is the

most likely value to occur, followed by ‘C’, then ‘A’. To optimize a CASE

statement for f ieldx , code the CASE statement as follows:

CASE f ieldx .

WHEN ‘B’. “Most likely value ....

WHEN ‘C’. “Next most likely value ....

WHEN ‘A’. “Least likely value ....

ENDCASE.




3.7 Subrout ine / func t ion performance

Because of the added overhead of calling subroutines, functions, etc.,

you should avoid the following style of coding:

Use:

IF f ield NE 0.

PERFORM SUB1.

ENDIF.

FORM SUB1.

....

ENDFORM.

rather than:

PERFORM SUB1.

FORM SUB1.

IF f ield NE 0.....

ENDIF.

ENDFORM.




3.8 Hard-cod ing Text (messages , repor t ou tpu t, etc..)

DON’T ! Wherever possible, all text to be passed to messages, or to bewritten to a report should be created as Text Symbols. This allows text to

be more easily maintained and supports the maintenance of these texts in

other languages.

3.9 Checking Return Code

The return code should always be checked after any database table

read/update statements.

For SELECT ... ENDSELECT processing loops, the return code should

be checked after the ENDSELECT statement to check for the success of

the SELECT statement.

For LOOP AT ... ENDLOOP processing loops, the return code should be

checked after the ENDLOOP statement to check for the success of the

LOOP statement.




4 String manipulations

4.1 Special operators

Use the special operators CO, CA etc. instead of programming theoperation yourself. Especially on long strings, ABAP statements per

character can cause high CPU consumption.

4.2 CONCATENATE

Instead of programming a string concatenation of your own, use the

CONCATENATE statement.

Also, make use of the SPLIT statement or the STRLEN function whenever

you need to split a string into several components or have to determine

the length of a string.

4.3 Deleting leading spaces

If you want to delete the leading spaces in a string, use the ABAP

statement SHIFT … LEFT DELETING LEADING …

Avoid in any case using SHIFT inside a WHILE loop.




CONCLUSION

Using these techniques we can optimize our code and increase the

performance of our program effectively.




EXERCISE

1. SELECT SINGLE * is more efficient than________________________

Whenever the full key of a table is known.

2. Reading an ____________table is faster than reading a database table.

3. If you are not processing the entire internal table use _____________

4. DESCRIBE TABLE i tab LINES f ield is ued to ____________________.

5. _______________allows text to be more easily maintained and supportsthe maintenance of these texts in other languages.

6.____________ system variable used to check the return code.

7. To delete duplicate entries from an internal table__________ statement

is used.8. ABAP reports that issue INSERT, UPDATE or DELETE commands have

to issue _____________statement.




SOLUTION

1. SELECT * … ENDSELECT

2. Internal table

3. BINARY SEARCH

4. to count up the number of entries in an internal table

5. TEXT SYMBOLS

6. SY-SUBRC

7. DELETE ADJACENT DUPLICATES

8. COMMIT WORK

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