topic Re: Structure and Internal Table in Application Development and Automation Discussions

Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:38:18 GMT

What R the differences between Structure and Internal table

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:41:42 GMT

Structure meant for GLOBAL EXISTANCE(these could be used by any other program without creating it again).

Structures are used especially to define the data at the interface of module pools and screens and to define the types of function module parameters.

Structures that are used more than once can be changed centrally because they were defined centrall. The active ABAP Dictionary makes this change at all relevant locations. ABAP programs or screen templates that use a

structure are automatically adjusted when the structure changes.

tables: There is a physical table on the database for each transparent table.

The names of the physical tables and the logical table definition in the ABAP/4 Dictionary correspond.

All business data and application data are stored in transparent tables.

Rewar dif usefull

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:42:29 GMT

Structure: Can be created in our ABAP data dictionary.

Internal table. The table can be created dynamically during execution of program and holds data at only execution time.

reward points if useful.

Regards,

Vimal

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:42:32 GMT

Re: What is the difference between internal table and structure?

Posted: Nov 5, 2007 9:49 AM in response to: mohammed raziq Reply E-mail this post

Internal tables are a standard data type object which exists only during the runtime of the program. They are used to perform table calculations on subsets of database tables and for re-organising the contents of database tables according to users need.

http://help.sap.com/saphelp_nw04/helpdata/en/fc/eb35de358411d1829f0000e829fbfe/content.htm

Difference between Work Area and Header Line

While adding or retrieving records to / from internal table we have to keep the record temporarily.

The area where this record is kept is called as work area for the internal table. The area must have the same structure as that of internal table. An internal table consists of a body and an optional header line.

Header line is a implicit work area for the internal table. It depends on how the internal table is declared that the itab will have the header line or not.

e.g.

data: begin of itab occurs 10,

ab type c,

cd type i,

end of itab. " this table will have the header line.

data: wa_itab like itab. " explicit work area for itab

data: itab1 like itab occurs 10. " table is without header line.

The header line is a field string with the same structure as a row of the body, but it can only hold a single row.

It is a buffer used to hold each record before it is added or each record as it is retrieved from the internal table. It is the default work area for the internal table

1) The difference between

whih header line and with out heater line of internal table.

ex:-

a) Data : itab like mara occurs 0 with header line.

b) Data: itab like mara occurs 0.

-While adding or retrieving records to / from internal table we have to keep the record temporarily.

-The area where this record is kept is called as work area for the internal table.

-The area must have the same structure as that of internal table. An internal table consists of a body and an optional header line.

-Header line is a implicit work area for the internal table. It depends on how the internal table is declared that the itab will have the header line or not.

a) Data : itab like mara occurs 0 with header line.

table is with header line

b) Data: itab like mara occurs 0.

table is without header line

2)work area / field string and internal table

which one is prefarable for good performance any why ?

-The header line is a field string with the same structure as a row of the body, but it can only hold a single row , whereas internal table can have more than one record.

In short u can define a workarea of an internal table which means that area must have the same structure as that of internal table and can have one record only.

Example code:

data: begin of itab occurs 10,

ab type c,

cd type i,

end of itab. " this table will have the header line.

data: wa_itab like itab. " explicit work area for itab

data: itab1 like itab occurs 10. " table is without header line.

Structure:

Structures are used to define the data at the interface of module pools and screens and to define the parameter types of function modules.

The central definition of structures that are used more than once makes it possible for them to be changed centrally. The active ABAP Dictionary then makes this change wherever required. ABAP programs or screen templates that use a structure are automatically adjusted when the structure is changed.

There are Flat, nested and deep structures. A flag structure only references elementary types. A nested structure references at least one further structure, but not a table type. A deep structure references at least one table type.

In a database table, you can only include flat structures as substructures.

A structure can have elements from different tables and structures. They do work similar to tables.

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:44:58 GMT

HI VINAY

Structures

A structure is a sequence of any elementary types, reference types, or complex data types.

You use structures in ABAP programs to group work areas that logically belong together. Since the elements of a structure can have any data type, structures can have a large range of uses. For example, you can use a structure with elementary data types to display lines from a database table within a program. You can also use structures containing aggregated elements to include all of the attributes of a screen or control in a single data object.

The following terms are important when we talk about structures:

Nested and non-nested structures

Flat and deep structures

A nested structure is a structure that contains one or more other structures as components. Flat structures contain only elementary data types with a fixed length (no internal tables, reference types, or strings). The term deep structure can apply regardless of whether the structure is nested or not. Nested structures are flat so long as none of the above types is contained in any nesting level.

Any structure that contains at least one internal table, reference type, or string as a component (regardless of nesting) is a deep structure. Accordingly, internal tables, references, and strings are also known as deep data types. The technical difference between deep structures and all others is as follows. When you create a deep structure, the system creates a pointer in memory that points to the real field contents or other administrative information. When you create a flat data type, the actual field contents are stored with the type in memory. Since the field contents are not stored with the field descriptions in the case of deep structures, assignments, offset and length specifications and other operations are handled differently from flat structures.

Internal Tables

Internal tables consists of a series of lines that all have the same data type. Internal tables are characterized by:

The line type, which can be any elementary type, reference type, or complex data type.

The key identifies table rows. It is made up of the elementary fields in the line. The key can be unique or non-unique.

The access method determines how ABAP will access individual table entries. There are three access types, namely unsorted tables, sorted index tables and hash tables. For index tables, the system maintains a linear index, so you can access the table either by specifying the index or the key.

Hashed tables have no linear index. You can only access hashed tables by specifying the key. The system has its own hash algorithm for managing the table.

You should use internal tables whenever you need to use structured data within a program. One imprint use is to store data from the database within a program.

Reward if helpful........................

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 06:50:42 GMT

Hi Rao,

PLZ refer this

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.

If its usefull reward points .

Thanks and Regards .

Arun.

Re: Structure and Internal Table

Former Member — Tue, 20 Nov 2007 07:00:38 GMT

Hi,Vinay.

As far as I know, Structure only store a few records, while Internal table can store many records, including Structure.

Regards,

feng.