efficient abap4 coding techniques

8/7/2019 efficient abap4 coding techniques

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Efficient ABAP 4 Programming Technique:----

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

ABAP/4. The following topics are covered.

Processing Database tables

Processing internal tables

M iscellaneous

String Manipulation

1 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 logical

database, selection can be restricted by using the CHECK statement

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

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.


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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 tables 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:


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SELECT * FROM T001GWHERE BUKRS EQ US01

AND TXTKO LIKE __PERS%.

....

ENDSELECT.

is more efficient than:SELECT * FROM T001GWHERE BUKRS EQ US01.

CHECK T001G-TXTKO+2(4) = PERS.

....ENDSELECT.

1.5 SELECT ,

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 andcustomer 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 accessedmultiple 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


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SELECT INTO

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 program

instead 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 the

application server. However, if an index exists on the table that can be

used for the sorting then the SELECT ORDER BY doesnt cause any

undue strains on the system.

1.9 Aggregate Functions

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 bymaterial 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 period

of time.


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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 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 Filling


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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_ fie ld LIKE itab-field1,

BEGIN OF itab OCCURS 100,field1(5), field2(5),

END OF itab.

compare_field = .

LOOP AT itab WHERE fie ld1 =comp are_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.


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2.4 Sorting

Wherever possible, identify the fields to be sorted. The format:SORT itab BY field1 field2.

is more efficient than:

SORT itab.SORT itab without fields specified attempts to sort the table by all fieldsother 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 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 dont need any of

the fields from the record then use the addition

TRANSPORTING NO FIELDS

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

TRANSPORTING

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[].


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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 records

that 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 field1field2 ]


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3 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 structure 1 TO structure2.

3.2 Determining the length of a string.

Use:fieldlength= STRLEN( field).

rather than:IF fie ld 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 .

Is more efficient than:

ASSIGN (KNA1-NAME1) TO .

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 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.


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....

ENDIF.is more efficient than:

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 f ield = value2.

....ENDIF.

or:

CASE field.

WHENvalue1.....

WHENvalue2.....

WHENvalue3.....

WHEN value n.

....ENDCASE.

The first (IF.ENDIF) 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 Optimizing IF and CASE structures

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

likelihood of each value occurring .

For example, field x 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 fie ld x, code the CASE statement as

follows:

CASE field x.WHEN B.


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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.

IFfield NE 0.....

ENDIF.ENDFORM.

3.8 Hard-coding Text (messages, report output, etc..)

DONT !

Wherever possible, all text to be passed to messages, or to be written 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.


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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

String manipulations

4.1 Special operators

Use 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 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 ABAPstatement SHIFT LEFT DELETING LEADING Avoid in any case using SHIFT inside a WHILE loop.

CONCLUSIONUsing these techniques we can optimize our code and increase the

performance of our program effectively.


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EXERCISE

1. SELECT SINGLE * is more efficient than________________________ Whenever the full key ofa 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 used 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 table5. TEXT SYMBOLS

6. SY-SUBRC

7. DELETE ADJACENT DUPLICATES

8. COMMIT WORK


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efficient abap4 coding techniques