SAP AND ABAP TIPS AND FACTS

Thursday, March 27, 2008

Internal Tables in SAP ABAP

Internal Tables in SAP ABAP

Internal tables are an important part of any ABAP development. Internal tables are used every where. We will see how to Initialize an internal table. 

Basically we will see what the following statements do to an internal table.

CLEAR
REFRESH
FREE

Consider an Internal table with name ITAB. If you want to clear the header line of the Internal Table ITAB use the statement given below

CLEAR ITAB.

Many a times you want to just clear the header line of the internal table but want to keep the contents as they are. CLEAR ITAB will just clear the header line of the internal table.

CLEAR ITAB[]

The above statement will clear the contents of the internal table but the header line contents will not be cleared.

REFRESH ITAB

The above statement will also clear the contents of the internal table completely. If the table has a header line the contents of the header line will still remain. This is used when the internal table is without the header line.

FREE ITAB

Will deallocate the memory for the internal table. For better performance of ABAP programs you should free the memory if the internal table is not going to be used again in the program.

DELETE

You can use DELETE statement to delete a particular record from the internal table.

 
Examples

CLEAR ITAB.

 If the ITAB has 4 fileds and 4 Records as follows

 

VBELN            KUNNR             MATNR             WERKS

00010              7777                 A123                  1000

00020              7777                 B122                  1000

00030              7777                 C506                  1000

00040              7777                 D777                  1000

 

and the header line contents are as follows

 

Header Line           <00010 7777  A123  1000>

 

Note: CLEAR ITAB will clear only the contents of the header line. and the ITAB values will remain as shown below.

ITAB

 

VBELN           KUNNR           MATNR           WERKS

00010             7777               A123                1000

00020             7777               B122                1000

00030             7777               C506                1000

00040             7777               D777                1000

Header Line <                             >

 

CLEAR ITAB[]

Will clear the header line as well as the contents of ITAB

VBELN KUNNR MATNR WERKS

<>

Header Line

Header Line           <00010 7777  A123  1000>

REFRESH

Will clear the header line as well as the contents of ITAB

VBELN KUNNR MATNR WERKS

Header Line           <00010 7777  A123  1000>

Header Line

<>

FREE ITAB 

Will clear the contents of the ITAB as shown above for REFRESH and CLEAR in addidtion to that it also frees the memory allocation from SAP memory.

Header Line           <00010 7777  A123  1000>

DELETE

If you just want to delete a particular row then you need to use the DELETE statement.

Example

DELETE ITAB INDEX IDX.

SY-SUBRC = 0 The entry was deleted.

SY_SUBRC = 4 The entry does not exist.

Consider a case when your internal table has duplicate entries, in this situation you can SORT the internal table and delete the duplicate entries as follows

SORT ITAB

DELETE ADJACENT DUPLICATES FROM ITAB.

 COMPARING field1 field2

 COMPARING ALL FIELDS


Related Interview Questions

1) IF ITAB is an internal table with a header line declared in ABAP what is the difference between the following

CLEAR ITAB
CLEAR ITAB[]
REFRESH ITAB
FREE ITAB

Ans. CLEAR ITAB will clear the contents of the header line only.
        CLEAR ITAB[] will clear the contents of the table but the header line contents will remain as they are.
        REFRESH ITAB will clear the contents of the table but the header line contents will remain as they are.FREE ITAB will clear the
        contents  of the ITAB keeping the header line contents intact. This will also dealocate the internal table from the SAP memory.

2 How ill you delete adjacent duplicates from an internal table ITAB

Ans. First you need to SORT the internal table as shown below
        SORT ITAB.
Then you need to delete the duplicates as shown below
        DELETE ADJACENT DUPLICATES FROM ITAB

Also

DELETE ADJACENT DUPLICATES FROM ITAB COMPARING field1 field2

DELETE ADJACENT DUPLICATES FROM ITAB COMPARING ALL FIELDS


       

  

ABAP TIPS

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 ABAP TIPS


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 ABAP TIPS
Always specify your conditions in the Where-clause instead of checking them yourself with check statements. The database system can then use an index (if possible) and the network load is considerably less.


 ABAP TIPS
For all frequently used Select statements, try to use an index. You always use an index if you specify (a generic part of) the index fields concatenated with logical Ands in the Select statement's Where clause. Note that complex Where clauses are poison for the statement optimizer in any database system.


 ABAP TIPS
If there exists at least one row of a database table or view with a certain condition, use the Select Single statement instead of a Select-Endselect-loop. Select Single requires one communication with the database system, whereas Select-Endselect needs two.


 ABAP TIPS
It is always faster to use the Into Table version of a Select statement than to use Append statements.


 ABAP TIPS
To read data from several logically connected tables use a join instead of nested Select statements. Network load is considerably less.


 ABAP TIPS
If you want to find the maximum, minimum, sum and average value or the count of a database column, use a select list with aggregate functions instead of computing the aggregates yourself. Network load is considerably less.


 ABAP TIPS
If you process your data only once, use a Select-Endselect-loop instead of collecting data in an internal table with Select Into Table. Internal table handling takes up much more space.


 ABAP TIPS
Use a select list or a view instead of Select * , if you are only interested in specific columns of the table. Network load is considerably less.


 ABAP TIPS
For all frequently used, read-only tables, try to use SAP buffering. Network load is considerably less.


 ABAP TIPS
Whenever possible, use array operations instead of single-row operations to modify your database tables. Frequent communication between the application program and database system produces considerable overhead.


 ABAP TIPS
Whenever possible, use column updates instead of single-row updates to update your database tables. Network load is considerably less.


 ABAP TIPS
Instead of using nested Select loops or FOR ALL ENTRIES it is often possible to use subqueries. Network load is considerably less.


 ABAP TIPS
Use the special operators CO, CA, CS, instead of programming the operations yourself. If ABAP/4 statements are executed per character on long strings, CPU consumption can rise substantially.


 ABAP TIPS
Some function modules for string manipulation have become obsolete and should be replaced by ABAP/4 statements or functions: STRING_CONCATENATE... -> CONCATENATE, STRING_SPLIT... -> SPLIT, STRING_LENGTH -> strlen(), STRING_CENTER -> WRITE...TO...CENTERED, STRING_MOVE_RIGHT -> WRITE...TO...RIGHT-JUSTIFIED


 ABAP TIPS
Use the CONCATENATE statement instead of programming a string concatenation of your own.


 ABAP TIPS
If you want to delete the leading spaces in a string, use the ABAP/4 statement SHIFT...LEFT DELETING LEADING... .Other constructions (with CN and SHIFT...BY SY-FDPOS PLACES, with CONDENSE if possible, with CN and ASSIGN CLA+SY-FDPOS(LEN) ...) are not as fast. In any case, avoid using SHIFT inside a WHILE-loop!


 ABAP TIPS
Use the SPLIT statement instead of programming a string split yourself.


 ABAP TIPS
Use the strlen( ) function to restrict the DO loop to the relevant part of the field, e.g. when determinating a check-sum.


 ABAP TIPS
Use "CLEAR f WITH val" whenever you want to initialize a field with a value different from the field's type-specific initial value.


 ABAP TIPS
Try to keep the table ordered and use binary search or used a table of type SORTED TABLE. If TAB has n entries, linear search runs in O( n ) time, whereas binary search takes only O( log2( n ) ).


 ABAP TIPS
A dynamic key access is slower than a static one, since the key specification must be evaluated at runtime. However, for large tables the costs are dominated by number of comparison needed to locate the entry.


 ABAP TIPS
If you need to access an internal table with different keys repeatedly, keep your own secondary indices.With a secondary index, you can replace a linear search with a binary search plus an index access.


 ABAP TIPS
LOOP ... WHERE is faster than LOOP/CHECK because LOOP ... WHERE evaluates the specified condition internally. As with any logical expressions, the performance is better if the operands of a comparison share a common type. The performance can be further enhanced if LOOP ... WHERE is combined with FROM i1 and/or TO i2, if possible.


Always use Pretty Printer and Extended Program Check before releasing the code. Do not leave unused code in the program. Comment the code thoroughly. Align the comments and the Code. Follow the SAP Standards and SAP Best Practices guidelines. It’s a good practice to take a dump of the code on your local drive.

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