24-Efficient ABAP Coding

Efficient ABAP/4 Coding TechniquesEfficient 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 Tables1 Processing Database Tables

1.1 Reading through 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 than a set of nested SELECT ... ENDSELECT statements.

1.2 Checking SELECT-OPTIONS when reading via 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-option(s) or CHECK condition).


In this case, a CHECK statement that returns a negative result terminatesthe 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 dbtab WHERE …. (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 a WHERE clause will make the SELECT statement more efficient than checking values after the select.


1.4 Selecting 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 T001G WHERE BUKRS EQ ‘US01’ AND TXTKO LIKE ‘__PERS%’.

....ENDSELECT.


SELECT * FROM T001G WHERE 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 only retrieve 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 ROWSIf 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 andthen checking for the system variable SY-DBCNT.

1.7 SELECT INTO TABLEReading 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 structurefor which you would otherwise use nested SELECTsInstead of processing a

SELECT … INTO <itab-fields>APPEND ITABENDSELECT


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 onthe database server affects the performance of all users on the system,whereas the sorting within the ABAP program ‘only’ affects the application 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 Aggregate FunctionsInstead 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 without WHERE

Coding a SELECT statement without a WHERE condition is only allowed for very small tables (e.g. customizing settings). For all other tables this is not permitted as performance problems will occur within a short periodof 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 is completed. Missing COMMITs can lead to bottlenecks on the databaseside because the system has to keep track of the table changes viarollback segments (in order to enable a rollback of all changes since thelast commit). Rollback segments are kept in memory and missingCOMMITs can lead to overflows of the rollback segment areas. Also thedatabase system holds locks on the changed records that are notreleased until COMMIT time.


2. Processing Internal Tables2. Processing Internal Tables

2.1 Filling

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 itab.

rather than:

SELECT * FROM dbtab. MOVE dbtab TO itab. APPEND itab.ENDSELECT.

To fill an internal table without creating duplicate entries and add up thePacked, Integer, and Floating Point fields at the same time, use:

COLLECT itab.


2.2 Sequential Reads

If you are reading through an internal table sequentially using the LOOP at itab ... 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_field LIKE itab-field1. BEGIN OF itab OCCURS 100, field1(5), field2(5), END OF itab. compare_field = <value to compare>.

LOOP AT itab WHERE field1 = compare_field. ... ENDLOOP.


2.3 Direct Reads

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

READ TABLE itab WITH KEY key BINARY SEARCH.

rather than:

READ TABLE itab WITH KEY key

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

The first method performs a binary search to find a matching record, but the table must be sorted first.


2.4 Sorting

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

SORT itab BY field1 field2.


SORT itab.

SORT itab without fields specified attempts to sort the table by all fields other than Packed, Integer, and Floating Point fields.

2.5 Counting Entries

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

DESCRIBE TABLE itab LINES field.

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


rather than:

LOOP AT itab. W_COUNT = W_COUNT + 1.

ENDLOOP.

2.6 Reading 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 theREAD TABLE T_VBAK WITH KEY VBELN = W_VBELN BINARY SEARCHstatement.If you only want to verify the existence of a record but don’t need any ofthe fields from the record then use the addition

TRANSPORTING 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 internal 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 following statement:

ITAB2[] = ITAB1[].

2.8 Appending 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 Looping at internal tables

If you are looping at an internal table just to count the number of recordsthat fulfill certain criteria then use the following variant of the loop statement:

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 DUPLICATE 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 field1 field2 …]


3 Miscellaneous3 Miscellaneous

3.1 Moving data from one table work area/structure to another one with an identical structure.

Use:MOVE structure1 TO structure2.

rather than:

MOVE-CORRESPONDING structure1 TO structure2.

3.2 Determining the length of a string.

Use:fieldlength = STRLEN( field ).

rather than:

IF field CP ‘#’.ENDIF.

fieldlength = 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) iscarried out only in the Data Dictionary and not in the symbol table. Thefield 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 Testing for Initial 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 by comparing 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 for multiple values

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

IF field = value1. ....ELSEIF field = value2. ....ENDIF.

or:CASE field.

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 associatedwith the CASE statement dictates that its use should be applied for levelsof three or greater.

3.6 Optimizing IF and CASE structures

To optimize IF and CASE structures, always test values in order of the likelihood of each value occuring.

For example, fieldx can have values ‘A’, ‘B’, or ‘C’. A value of ‘B’ is themost likely value to occur, followed by ‘C’, then ‘A’. To optimize a CASEstatement for fieldx, code the CASE statement as follows:

CASE fieldx. WHEN ‘B’. “Most likely value .... WHEN ‘C’. “Next most likely value .... WHEN ‘A’. “Least likely value ....ENDCASE.


3.7 Subroutine / function performance

Because of the added overhead of calling subroutines, functions, etc.,you should avoid the following style of coding:

Use:IF field NE 0. PERFORM SUB1.ENDIF.

FORM SUB1. ....

ENDFORM.rather than:

PERFORM SUB1.

FORM SUB1. IF field NE 0. .... ENDIF.ENDFORM.


3.8 Hard-coding Text (messages, report output, 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 tobe more easily maintained and supports the maintenance of these texts

inother 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 4 String manipulationsString manipulations

4.1 Special operatorsUse the special operators CO, CA etc. instead of programming the operation yourself. Especially on long strings, ABAP statements per character can cause high CPU consumption.

4.2 CONCATENATEInstead of programming a string concatenation of your own, use theCONCATENATE statement.Also, make use of the SPLIT statement or the STRLEN function wheneveryou need to split a string into several components or have to determine the length of a string.

4.3 Deleting leading spacesIf 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.


CONCLUSIONCONCLUSION

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 itab LINES field is ued to ____________________.

5. _______________allows text to be more easily maintained and

supports

the 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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24-Efficient ABAP Coding