Internal table objects

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Internal table objects

Internal tables are dynamic variable data objects. Like all variables, you declare them using the DATA statement. You can also declare static
internal tables in procedures using the STATICS statement, and static internal tables in classes using the CLASS-DATA statement. This
description is restricted to the DATA statement. However, it applies equally to the STATICS and CLASS-DATA statements.

Reference to Declared Internal Table Types

Like all other data objects, you can declare internal table objects using the LIKE or TYPE addition of the DATA statement.

DATA TYPE |LIKE [WITH HEADER LINE].

Here, the LIKE addition refers to an existing table object in the same program. The TYPE addition can refer to an internal type in the
program declared using the TYPES statement, or a table type in the ABAP Dictionary.

You must ensure that you only refer to tables that are fully typed. Referring to generic table types (ANY TABLE, INDEX TABLE) or not
specifying the key fully is not allowed (for exceptions, refer to Special Features of Standard Tables).

The optional addition WITH HEADER line declares an extra data object with the same name and line type as the internal table. This data
object is known as the header line of the internal table. You use it as a work area when working with the internal table (see Using the
Header Line as a Work Area). When you use internal tables with header lines, you must remember that the header line and the body of the
table have the same name. If you have an internal table with header line and you want to address the body of the table, you must indicate
this by placing brackets after the table name ([]). Otherwise, ABAP interprets the name as the name of the header line and not of the
body of the table. You can avoid this potential confusion by using internal tables without header lines. In particular, internal tables nested
in structures or other internal tables must not have a header line, since this can lead to ambiguous expressions.


TYPES VECTOR TYPE SORTED TABLE OF I WITH UNIQUE KEY TABLE LINE.

DATA: ITAB TYPE VECTOR,
JTAB LIKE ITAB WITH HEADER LINE.

* MOVE ITAB TO JTAB. <- Syntax error!

MOVE ITAB TO JTAB[].

The table object ITAB is created with reference to the table type VECTOR. The table object JTAB has the same data type as ITAB. JTAB also
has a header line. In the first MOVE statement, JTAB addresses the header line. Since this has the data type I, and the table type of ITAB
cannot be converted into an elementary type, the MOVE statement causes a syntax error. The second MOVE statement is correct, since
both operands are table objects.

Declaring New Internal Tables

You can use the DATA statement to construct new internal tables as well as using the LIKE or TYPE addition to refer to existing types or
objects. The table type that you construct does not exist in its own right; instead, it is only an attribute of the table object. You can refer to
it using the LIKE addition, but not using TYPE. The syntax for constructing a table object in the DATA statement is similar to that for defining
a table type in the TYPES statement.

DATA TYPE|LIKE OF WITH
[INITIAL SIZE ]
[WITH HEADER LINE].

As when you define a table type , the type constructor

OF WITH

defines the table type , the line type , and the key of the internal table . Since the technical attributes of
data objects are always fully specified, the table must be fully specified in the DATA statement. You cannot create generic table types (ANY
TABLE, INDEX TABLE), only fully-typed tables (STANDARD TABLE, SORTED TABLE, HASHED TABLE). You must also specify the key and whether
it is to be unique (for exceptions, refer to Special Features of Standard Tables).

As in the TYPES statement, you can, if you wish, allocate an initial amount of memory to the internal table using the INITIAL SIZE addition.
You can create an internal table with a header line using the WITH HEADER LINE addition. The header line is created under the same
conditions as apply when you refer to an existing table type.



DATA ITAB TYPE HASHED TABLE OF SPFLI
WITH UNIQUE KEY CARRID CONNID.

The table object ITAB has the type hashed table, a line type corresponding to the flat structure SPFLI from the ABAP Dictionary, and a
unique key with the key fields CARRID and CONNID. The internal table ITAB can be regarded as an internal template for the database table
SPFLI. It is therefore particularly suitable for working with data from this database table as long as you only access it using the key.

Internal table types

This section describes how to define internal tables locally in a program. You can also define internal tables globally as data types in the
ABAP Dictionary.

Like all local data types in programs , you define internal tables using the TYPES statement. If you do not refer to an existing table type
using the TYPE or LIKE addition, you can use the TYPES statement to construct a new local internal table in your program.

TYPES TYPE|LIKE OF [WITH ]
[INITIAL SIZE ].

After TYPE or LIKE, there is no reference to an existing data type. Instead, the type constructor occurs:

OF [WITH ]

The type constructor defines the table type , the line type , and the key of the internal table .

You can, if you wish, allocate an initial amount of memory to the internal table using the INITIAL SIZE addition.

Table type

You can specify the table type as follows:

Generic table types

INDEX TABLE

For creating a generic table type with index access.

ANY TABLE

For creating a fully-generic table type.

Data types defined using generic types can currently only be used for field symbols and for interface parameters in procedures . The generic
type INDEX TABLE includes standard tables and sorted tables. These are the two table types for which index access is allowed. You cannot
pass hashed tables to field symbols or interface parameters defined in this way. The generic type ANY TABLE can represent any table. You
can pass tables of all three types to field symbols and interface parameters defined in this way. However, these field symbols and
parameters will then only allow operations that are possible for all tables, that is, index operations are not allowed.

Fully-Specified Table Types

STANDARD TABLE or TABLE

For creating standard tables.

SORTED TABLE

For creating sorted tables.

HASHED TABLE

For creating hashed tables.

Fully-specified table types determine how the system will access the entries in the table in key operations. It uses a linear search for
standard tables, a binary search for sorted tables, and a search using a hash algorithm for hashed tables.

Line type

For the line type , you can specify:

Any data type if you are using the TYPE addition. This can be a predefined ABAP type, a local type in the program, or a data type from the
ABAP Dictionary. If you specify any of the generic elementary types C, N, P, or X, any attributes that you fail to specify (field length, number
of decimal places) are automatically filled with the default values. You cannot specify any other generic types.
Any data object recognized within the program at that point if you are using the LIKE addition. The line type adopts the fully-specified data
type of the data object to which you refer. Except for within classes, you can still use the LIKE addition to refer to database tables and
structures in the ABAP Dictionary (for compatibility reasons).
All of the lines in the internal table have the fully-specified technical attributes of the specified data type.

Key

You can specify the key of an internal table as follows:

[UNIQUE|NON-UNIQUE] KEY ...

In tables with a structured line type, all of the components belong to the key as long as they are not internal tables or references,
and do not contain internal tables or references. Key fields can be nested structures. The substructures are expanded component by
component when you access the table using the key. The system follows the sequence of the key fields.

[UNIQUE|NON-UNIQUE] KEY TABLE LINE

If a table has an elementary line type (C, D, F, I, N, P, T, X), you can define the entire line as the key. If you try this for a table whose line
type is itself a table, a syntax error occurs. If a table has a structured line type, it is possible to specify the entire line as the key. However,
you should remember that this is often not suitable.

[UNIQUE|NON-UNIQUE] DEFAULT KEY

This declares the fields of the default key as the key fields. If the table has a structured line type, the default key contains all non-numeric
columns of the internal table that are not and do not contain references or internal tables. If the table has an elementary line type, the
default key is the entire line. The default key of an internal table whose line type is an internal table, the default key is empty.

Specifying a key is optional. If you do not specify a key, the system defines a table type with an arbitrary key. You can only use this to
define the types of field symbols and the interface parameters of procedures . For exceptions, refer to Special Features of Standard Tables.

The optional additions UNIQUE or NON-UNIQUE determine whether the key is to be unique or non-unique, that is, whether the table can
accept duplicate entries. If you do not specify UNIQUE or NON-UNIQUE for the key, the table type is generic in this respect. As such, it can
only be used for specifying types. When you specify the table type simultaneously, you must note the following restrictions:

You cannot use the UNIQUE addition for standard tables. The system always generates the NON-UNIQUE addition automatically.
You must always specify the UNIQUE option when you create a hashed table.
Initial Memory Requirement

You can specify the initial amount of main memory assigned to an internal table object when you define the data type using the following
addition:

INITIAL SIZE

This size does not belong to the data type of the internal table, and does not affect the type check. You can use the above addition to
reserve memory space for table lines when you declare the table object.

When this initial area is full, the system makes twice as much extra space available up to a limit of 8KB. Further memory areas of 12KB each
are then allocated.

You can usually leave it to the system to work out the initial memory requirement. The first time you fill the table, little memory is used. The
space occupied, depending on the line width, is 16 <= <= 100.

It only makes sense to specify a concrete value of if you can specify a precise number of table entries when you create the table and
need to allocate exactly that amount of memory (exception: Appending table lines to ranked lists). This can be particularly important for
deep-structured internal tables where the inner table only has a few entries (less than 5, for example).

To avoid excessive requests for memory, large values of are treated as follows: The largest possible value of is 8KB divided by the
length of the line. If you specify a larger value of , the system calculates a new value so that n times the line width is around 12KB.

Examples



TYPES: BEGIN OF LINE,
COLUMN1 TYPE I,
COLUMN2 TYPE I,
COLUMN3 TYPE I,
END OF LINE.

TYPES ITAB TYPE SORTED TABLE OF LINE WITH UNIQUE KEY COLUMN1.

The program defines a table type ITAB. It is a sorted table, with line type of the structure LINE and a unique key of the component
COLUMN1.



TYPES VECTOR TYPE HASHED TABLE OF I WITH UNIQUE KEY TABLE LINE.

TYPES: BEGIN OF LINE,
COLUMN1 TYPE I,
COLUMN2 TYPE I,
COLUMN3 TYPE I,
END OF LINE.

TYPES ITAB TYPE SORTED TABLE OF LINE WITH UNIQUE KEY COLUMN1.

TYPES: BEGIN OF DEEPLINE,
FIELD TYPE C,
TABLE1 TYPE VECTOR,
TABLE2 TYPE ITAB,
END OF DEEPLINE.

TYPES DEEPTABLE TYPE STANDARD TABLE OF DEEPLINE
WITH DEFAULT KEY.

The program defines a table type VECTOR with type hashed table, the elementary line type I and a unique key of the entire table line. The
second table type is the same as in the previous example. The structure DEEPLINE contains the internal table as a component. The table
type DEEPTABLE has the line type DEEPLINE. Therefore, the elements of this internal table are themselves internal tables. The key is the
default key - in this case the column FIELD. The key is non-unique, since the table is a standard table.

Creating Internal Tables

Like other elements in the ABAP type concept, you can declare internal tables as abstract data
types in programs or in the ABAP Dictionary, and then use them to define data objects.
Alternatively, you can define them directly as data objects. When you create an internal table as a
data object, you should ensure that only the administration entry which belongs to an internal
table is declared statically. The minimum size of an internal table is 256 bytes. This is important if an
internal table occurs as a component of an aggregated data object, since even empty internal
tables within tables can lead to high memory usage. (In the next functional release, the size of the
table header for an initial table will be reduced to 8 bytes). Unlike all other ABAP data objects, you
do not have to specify the memory required for an internal table. Table rows are added to and
deleted from the table dynamically at runtime by the various statements for adding and deleting
records.


You can create internal tables in different types.
You can create standard internal table and then make it sort in side the program.
The same way you can change to hashed internal tables also.
There will be some performance issues with regard to standard internal tables/ hashed internal
tables/ sorted internal tables.

Internal tables

Internal tables provide a means of taking data from a fixed structure and storing it in working memory in ABAP. The data is stored line by
line in memory, and each line has the same structure. In ABAP, internal tables fulfill the function of arrays. Since they are dynamic data
objects, they save the programmer the task of dynamic memory management in his or her programs. You should use internal tables
whenever you want to process a dataset with a fixed structure within a program. A particularly important use for internal tables is for
storing and formatting data from a database table within a program. They are also a good way of including very complicated data
structures in an ABAP program.

Like all elements in the ABAP type concept, internal tables can exist both as data types and as data objects A data type is the abstract
description of an internal table, either in a program or centrally in the ABAP Dictionary, that you use to create a concrete data object. The
data type is also an attribute of an existing data object.

Internal Tables as Data Types

Internal tables and structures are the two structured data types in ABAP. The data type of an internal table is fully specified by its line type,
key, and table type.

Line type

The line type of an internal table can be any data type. The data type of an internal table is normally a structure. Each component of the
structure is a column in the internal table. However, the line type may also be elementary or another internal table.

Key

The key identifies table rows. There are two kinds of key for internal tables - the standard key and a user-defined key. You can specify
whether the key should be UNIQUE or NON-UNIQUE. Internal tables with a unique key cannot contain duplicate entries. The uniqueness
depends on the table access method.

If a table has a structured line type, its default key consists of all of its non-numerical columns that are not references or themselves
internal tables. If a table has an elementary line type, the default key is the entire line. The default key of an internal table whose line type
is an internal table, the default key is empty.

The user-defined key can contain any columns of the internal table that are not references or themselves internal tables. Internal tables
with a user-defined key are called key tables. When you define the key, the sequence of the key fields is significant. You should remember
this, for example, if you intend to sort the table according to the key.

Table type

The table type determines how ABAP will access individual table entries. Internal tables can be divided into three types:

Standard tables have an internal linear index. From a particular size upwards, the indexes of internal tables are administered as trees. In
this case, the index administration overhead increases in logarithmic and not linear relation to the number of lines. The system can access
records either by using the table index or the key. The response time for key access is proportional to the number of entries in the table.
The key of a standard table is always non-unique. You cannot specify a unique key. This means that standard tables can always be filled
very quickly, since the system does not have to check whether there are already existing entries.

Sorted tables are always saved sorted by the key. They also have an internal index. The system can access records either by using the
table index or the key. The response time for key access is logarithmically proportional to the number of table entries, since the system
uses a binary search. The key of a sorted table can be either unique or non-unique. When you define the table, you must specify whether
the key is to be unique or not. Standard tables and sorted tables are known generically as index tables.

Hashed tables have no linear index. You can only access a hashed table using its key. The response time is independent of the number of
table entries, and is constant, since the system access the table entries using a hash algorithm. The key of a hashed table must be unique.
When you define the table, you must specify the key as UNIQUE.

Generic Internal Tables

Unlike other local data types in programs, you do not have to specify the data type of an internal table fully. Instead, you can specify a
generic construction, that is, the key or key and line type of an internal table data type may remain unspecified. You can use generic
internal tables to specify the types of field symbols and the interface parameters of procedures . You cannot use them to declare data
objects.

Internal Tables as Dynamic Data Objects

Data objects that are defined either with the data type of an internal table, or directly as an internal table, are always fully defined in
respect of their line type, key and access method. However, the number of lines is not fixed. Thus internal tables are dynamic data objects,
since they can contain any number of lines of a particular type. The only restriction on the number of lines an internal table may contain are
the limits of your system installation. The maximum memory that can be occupied by an internal table (including its internal administration)
is 2 gigabytes. A more realistic figure is up to 500 megabytes. An additional restriction for hashed tables is that they may not contain more
than 2 million entries. The line types of internal tables can be any ABAP data types - elementary, structured, or internal tables. The
individual lines of an internal table are called table lines or table entries. Each component of a structured line is called a column in the
internal table.

Choosing a Table Type

The table type (and particularly the access method) that you will use depends on how the typical internal table operations will be most
frequently executed.

Standard tables

This is the most appropriate type if you are going to address the individual table entries using the index. Index access is the quickest
possible access. You should fill a standard table by appending lines (ABAP APPEND statement), and read, modify and delete entries by
specifying the index (INDEX option with the relevant ABAP command). The access time for a standard table increases in a linear relationship
with the number of table entries. If you need key access, standard tables are particularly useful if you can fill and process the table in
separate steps. For example, you could fill the table by appending entries, and then sort it. If you use the binary search option with key
access, the response time is logarithmically proportional to the number of table entries.

Sorted tables

This is the most appropriate type if you need a table which is sorted as you fill it. You fill sorted tables using the INSERT statement. Entries
are inserted according to the sort sequence defined through the table key. Any illegal entries are recognized as soon as you try to add
them to the table. The response time for key access is logarithmically proportional to the number of table entries, since the system always
uses a binary search. Sorted tables are particularly useful for partially sequential processing in a LOOP if you specify the beginning of the
table key in the WHERE condition.

Hashed tables

This is the most appropriate type for any table where the main operation is key access. You cannot access a hashed table using its index.
The response time for key access remains constant, regardless of the number of table entries. Like database tables, hashed tables always
have a unique key. Hashed tables are useful if you want to construct and use an internal table which resembles a database table or for
processing large amounts of data.

Using Sorted table and Index while processing Internal tables

There would have been many instances where we would have to process large entries in an internal table with a WHERE condition. This article is intended to demonstrate the comparison between three different methods in handling this situation.

First Method: The normal method used by most of us. Standard internal table processing using WHERE condition

Second Method: Same as above, but here we would be using the Sorted table

Third Method: Sorted table and using the Index

Following is the demo program illustrating the above three methods:

REPORT ZINTERNAL_TABLE_OPERATIONS.

* Program to find the best method in reading the internal tables
* Author: Suresh Kumar Parvathaneni

* Type declaration
TYPES:
 BEGIN OF TY_MARA,
   MATNR LIKE MARA-MATNR,
   MTART LIKE MARA-MTART,
 END OF TY_MARA.

* Internal table declaration
DATA:
 T_MARA TYPE STANDARD TABLE OF TY_MARA,
 T_MARA1 TYPE SORTED TABLE OF TY_MARA
         WITH NON-UNIQUE KEY MTART.

* Variable declaration
DATA:
 W_COUNTER TYPE I,
 W_RUNTIME1 TYPE I,
 W_RUNTIME2 TYPE I,
 W_TABIX LIKE SY-TABIX.

* Table workarea definition
DATA:
 WA_MARA TYPE TY_MARA.

SELECT MATNR                           " Material Number
      MTART                           " Material Type
 FROM MARA
 INTO TABLE T_MARA.

T_MARA1[] = T_MARA[].

* CASE 1: Processing internal table using LOOP..WHERE Condition

GET RUN TIME FIELD W_RUNTIME1.

LOOP AT T_MARA INTO WA_MARA WHERE MTART EQ 'FHMI'.
 ADD 1 TO W_COUNTER.
ENDLOOP.

GET RUN TIME FIELD W_RUNTIME2.
* Calculate Runtime
W_RUNTIME2 = W_RUNTIME2 - W_RUNTIME1.
WRITE W_RUNTIME2.

CLEAR W_COUNTER.

* CASE 2: Using a Sorted table

GET RUN TIME FIELD W_RUNTIME1.
LOOP AT T_MARA1 INTO WA_MARA WHERE MTART EQ 'FHMI'.
 ADD 1 TO W_COUNTER.
ENDLOOP.

GET RUN TIME FIELD W_RUNTIME2.
* Calculate Runtime
W_RUNTIME2 = W_RUNTIME2 - W_RUNTIME1.
WRITE W_RUNTIME2.

CLEAR W_COUNTER.

* CASE 3: Using INDEX on a sorted table

GET RUN TIME FIELD W_RUNTIME1.
READ TABLE T_MARA1 INTO WA_MARA WITH KEY MTART = 'FHMI'.
IF SY-SUBRC EQ 0.
 W_TABIX = SY-TABIX + 1.
 ADD 1 TO W_COUNTER.
 LOOP AT T_MARA1 INTO WA_MARA FROM W_TABIX.
   IF WA_MARA-MTART NE 'FHMI'.
     EXIT.
   ENDIF.
   ADD 1 TO W_COUNTER.
 ENDLOOP.
ENDIF.
GET RUN TIME FIELD W_RUNTIME2.
* Calculate Runtime
W_RUNTIME2 = W_RUNTIME2 - W_RUNTIME1.
WRITE W_RUNTIME2.

Following is the analysis report in microseconds, as per the data volume:

Records: 21,390

Iteration No	Using Normal LOOP & WHERE	Using Sorted table LOOP & WHERE	Using INDEX on Sorted table
1	897	887	11
2	839	879	10
3	839	877	10
4	834	880	9
5	842	837	10

Records: 132,693

Iteration No	Using Normal LOOP & WHERE	Using Sorted table LOOP & WHERE	Using INDEX on Sorted table
1	34239	35774	3567
2	34271	38250	3592
3	34492	36534	3554
4	34198	35695	3584

Sorted table might have given a better performance here if the field in the WHERE condition is the first field in the internal table. However, from the above statistics, we can say that method 3 is better than the other 2 methods. In production environment, the data would be huge and the performance could be much improved with this simple technique.

Internal Table Performance Improvements

Using Parallel cursor

Using GroupBy