extra dataset

[Former Member]

what are extra data sets?please provide the answer.

[amit_khare]

Hi,

Since internal tables have fixed line structures, they are not suited to handle data sets with varying structures. Instead, you can use extract datasets for this purpose.

An extract is a sequential dataset in the memory area of the program. You can only address the entries in the dataset within a special loop. The index or key access permitted with internal tables is not allowed. You may only create one extract in any ABAP program. The size of an extract dataset is, in principle, unlimited. Extracts larger than 500KB are stored in operating system files. The practical size of an extract is up to 2GB, as long as there is enough space in the filesystem.

An extract dataset consists of a sequence of records of a pre-defined structure. However, the structure need not be identical for all records. In one extract dataset, you can store records of different length and structure one after the other. You need not create an individual dataset for each different structure you want to store. This fact reduces the maintenance effort considerably.

In contrast to internal tables, the system partly compresses extract datasets when storing them. This reduces the storage space required. In addition, you need not specify the structure of an extract dataset at the beginning of the program, but you can determine it dynamically during the flow of the program.

You can use control level processing with extracts just as you can with internal tables. The internal administration for extract datasets is optimized so that it is quicker to use an extract for control level processing than an internal table.

Procedure for creating an extract:

1. Define the record types that you want to use in your extract by declaring them as field groups. The structure is defined by including fields in each field group.

2. Fill the extract line by line by extracting the required data.

3. Once you have filled the extract, you can sort it and process it in a loop. At this stage, you can no longer change the contents of the extract.

Defining an Extract

To define an extract, you must first declare the individual records and then define their structure.

Declaring Extract Records as Field Groups

An extract dataset consists of a sequence of records. These records may have different structures. All records with the same structure form a record type. You must define each record type of an extract dataset as a field group, using the FIELD-GROUPS statement.

FIELD-GROUPS <fg>.

This statement defines a field group <fg>. A field group combines several fields under one name. For clarity, you should declare your field groups at the end of the declaration part of your program.

A field group does not reserve storage space for the fields, but contains pointers to existing fields. When filling the extract dataset with records, these pointers determine the contents of the stored records.

You can also define a special field group called HEADER:

FIELD-GROUPS HEADER.

This group is automatically placed before any other field groups when you fill the extract. This means that a record of a field group <fg> always contains the fields of the field group HEADER. When sorting the extract dataset, the system uses these fields as the default sort key.

Defining the Structure of a Field Group

To define the structure of a record, use the following statement to add the required fields to a field group:

INSERT <f1>... <f n> INTO <fg>.

This statement defines the fields of field group <fg>. Before you can assign fields to a field group, you must define the field group <fg> using the FIELD-GROUPS statement. The fields in the field group must be global data objects in the ABAP program. You cannot assign a local data object defined in a procedure to a field group.

The INSERT statement, just as the FIELD-GROUPS statement, neither reserves storage space nor transfers values. You use the INSERT statement to create pointers to the fields <f i > in the field group <fg>, thus defining the structures of the extract records.

When you run the program, you can assign fields to a field group up to the point when you use this field group for the first time to fill an extract record. From this point on, the structure of the record is fixed and may no longer be changed. In short, as long as you have not used a field group yet, you can still extend it dynamically.

The special field group HEADER is part of every extract record. Consequently, you may not change HEADER once you have filled the first extract record.

A field may occur in several field groups; however, this means unnecessary data redundancy within the extract dataset. You do not need to define the structure of a field group explicitly with INSERT. If the field group HEADER is defined, an undefined field group consists implicitly of the fields in HEADER, otherwise, it is empty.

Filling an Extract with Data

Once you have declared the possible record types as field groups and defined their structure, you can fill the extract dataset using the following statements:

EXTRACT <fg>.

When the first EXTRACT statement occurs in a program, the system creates the extract dataset and adds the first extract record to it. In each subsequent EXTRACT statement, the new extract record is added to the dataset.

Each extract record contains exactly those fields that are contained in the field group <fg>, plus the fields of the field group HEADER (if one exists). The fields from HEADER occur as a sort key at the beginning of the record. If you do not explicitly specify a field group <fg>, the

EXTRACT

statement is a shortened form of the statement

EXTRACT HEADER.

When you extract the data, the record is filled with the current values of the corresponding fields.

As soon as the system has processed the first EXTRACT statement for a field group <fg>, the structure of the corresponding extract record in the extract dataset is fixed. You can no longer insert new fields into the field groups <fg> and HEADER. If you try to modify one of the field groups afterwards and use it in another EXTRACT statement, a runtime error occurs.

By processing EXTRACT statements several times using different field groups, you fill the extract dataset with records of different length and structure. Since you can modify field groups dynamically up to their first usage in an EXTRACT statement, extract datasets provide the advantage that you need not determine the structure at the beginning of the program.

regards,

Amit

[Former Member]

ru reffering to read data from appl. server...

open dataset...

read dataset...

close dataset...

DATA: itab TYPE STANDARD TABLE OF mara,

wa_itab TYPE mara.

SELECT * FROM mara INTO TABLE itab WHERE matnr > '000000000000001000'

AND matnr < '000000000000009010'.

OPEN DATASET 'sharat.pm' FOR APPENDING IN TEXT MODE ENCODING DEFAULT.

IF sy-subrc = 0.

LOOP AT itab INTO wa_itab.

TRANSFER wa_itab-matnr TO 'sharat.pm'.

ENDLOOP.

ENDIF.

CLOSE DATASET 'sharat.pm'.