CREATING INTERNAL TABLES

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.

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.